Smallpox: Current, comprehensive information on pathogenesis, microbiology, epidemiology, diagnosis, treatment, and prophylaxis

Last updated February 6, 2009

Agent
Pathogenesis
Historical Perspective
Epidemiology
Use of Smallpox as a Biological Weapon
Clinical Features of Variola Major
—Ordinary Smallpox
—Flat-Type (Malignant) Smallpox
—Hemorrhagic Smallpox
—Smallpox in Children
Clinical Features of Variola Minor
Differential Diagnosis
—Differential Diagnosis of the Rash Illness
—Monkeypox
—Distinguishing Features Between Smallpox, Monkeypox, and Chickenpox
Determining the Likelihood of a Smallpox Diagnosis
Laboratory Diagnosis
—Specimen Collection and Handling
—Laboratory Response Network (LRN)
—Tests for Detection and Identification of Variola Virus
—Rapid Tests for Diagnosis of VZV and HSV
—Testing in Areas With Confirmed Smallpox
—Inadvertent Discovery of Variola Virus in a Laboratory Specimen
Treatment
Smallpox Vaccination
—Historical Perspective
—ACAM2000 Vaccine
—New Vaccines
—Recommendations for Use of Vaccinia Vaccines
—The US Smallpox Vaccination Program
—Vaccination Schedule
—Dosage and Route of Administration
—Local Reaction to Vaccination
—Contraindications and Precautions
—Vaccine Distribution and Storage
—Vaccination of Healthcare Workers
—Use of Vaccine for Postexposure Prophylaxis
—Use of Vaccine During a Smallpox Emergency
—Smallpox Vaccination Clinic Implementation
Adverse Events Following Smallpox Vaccination
—Historic Perspective
—Recent Experience
—Risk of Contact Vaccinia
—Treatment of Vaccine Adverse Reactions
—Liability Issues Following Smallpox Vaccine Administration
Infection Control
Issues Related to Autopsies and Burial
Public Health Reporting and Case Definitions
References

Agent

Variola virus classification:

DNA virus
Family Poxviridae, subfamily Chordopoxviridae, genus Orthopoxvirus

Virion morphology:

Brick-shaped virion approximately 200 nm in diameter, 250 to 300 nm long, and 250 nm high (see References: International Committee on Taxonomy of Viruses), about the size of a bacterial spore
Enveloped
Dumbbell-shaped core containing nucleic acid and surrounded by a series of membranes
Replicates in the cytoplasm of host cells, forming B-type inclusion bodies (Guarnieri bodies), unlike varicella or herpes viruses, which replicate in the nucleus

Genetic composition:

The genome is composed of a single, linear, double-stranded DNA covalently closed at each end.
Average genome has 200,000 base pairs (200 kbp) and is among the largest animal viruses.
The genome of several strains has been completely sequenced, and efforts are under way to assess the genetic diversity of existing variola viruses and differentiate them (see References: National Center for Biotechnology Information, LeDuc 2001, Gubser 2004). A Web-based poxvirus genomic resource database has been established (see References: Lefkowitz 2005).
Comparative genomic analysis of 45 epidemiologically varied variola virus isolates from the past 30 years indicates low sequence diversity, suggesting little difference in functional genes. Analysis of viral linear DNA suggests that variola evolution involved direct descent and DNA end-region recombination events (see References: Esposito 2006).

Variola viruses traditionally have been classified as variola major and variola minor on the basis of the severity of clinical illness caused by infection. Recognized variola minor strains include:

Alastrim
Amass
Kaffir

There are many viruses in the family Poxviridae with vertebrate host ranges that do not include humans; related viruses that can cause natural infections in humans include:

Other Orthopoxvirus species

Monkeypox virus
Vaccinia virus
Cowpox virus

Other Chordopoxviridae genera

Yatapoxviruses: tanapox virus, Yaba monkey tumor virus, and Yaba-like disease virus of monkeys
Parapoxviruses: Orf virus
Molluscipoxvirus: agent of molluscum contagiosum

Pathogenesis

The pathogenesis of smallpox involves the following steps (see References: Fenner 1988: Chapter 3; Henderson: Smallpox as a biological weapon):

The portal of entry for variola virus is usually through the oropharyngeal or respiratory mucosa; variola virus also can enter through the skin, and rarely, through the conjunctiva or placenta (see References: Fenner 1988: Chapters 1 and 3).
The virus migrates rapidly to regional lymph nodes.
Asymptomatic viremia occurs on the 3rd or 4th day after infection, with further dissemination of the virus to spleen, bone marrow, and other lymph nodes.
Secondary viremia occurs by the 8th to 12th day after initial infection; this is followed by onset of fever and toxemia.
The virus localizes in small blood vessels of the dermis and oropharyngeal mucosa, leading to initial onset of the enanthem and exanthem, at which point (about day 14) the patient becomes infectious. The spleen, lymph nodes, kidneys, liver, bone marrow, and other viscera also may contain large amounts of virus (see References: Breman 2002).
The development and evolution of skin lesions involves the following steps:

Dilatation of the capillaries in the papillary layer of the dermis occurs initially, followed by swelling of the endothelial cells in the vessel walls. Perivascular cuffing with lymphocytes, plasma cells, and macrophages can be seen.
Lesions then develop in the epidermis, where the cells become swollen and vacuolated; characteristic B-type inclusion bodies can be found in the cytoplasm.
The cells increase in size and the cell membranes rupture, leading to vesicular lesions.
Pustulation results from the migration of polymorphonuclear cells into the vesicle.
The contents of the pustule gradually become desiccated, leading to crusting or scabbing of the lesions.
Re-epithilialization and scarring occur as the lesions heal.

Death most commonly results from overwhelming toxemia, probably associated with circulating immune complexes.

Historical Perspective

Occurrence of Smallpox in the Pre-eradication Era

Smallpox likely originated in Egypt or India over 3,000 years ago (see References: WHO: Fact sheet on smallpox). Egyptian mummies dating from as early as 1500 BC showed characteristic pox-like skin lesions suggestive of smallpox.
Smallpox initially was introduced to the native populations of the Western Hemisphere by explorers from Europe and later by African slaves. The first recorded epidemic of smallpox in the New World occurred in 1507 on the island of Hispaniola (see References: Fenner 1988: Chapter 5). Eventually the disease spread throughout the hemisphere with devastating consequences for many native tribes.
By the mid-1700s, smallpox was a major endemic disease throughout the world, except in Australia, where it was first introduced in 1789 and again in 1829.
Following the famous observations of Edward Jenner at the end of the 18th century, vaccination against smallpox using cowpox virus became a widespread practice in Europe and the United States. During the 19th century, cowpox virus was gradually replaced by vaccinia virus as the agent used in vaccination (see Smallpox Vaccination: Historical Perspective). During the first half of the 20th century, smallpox vaccination using vaccinia virus was widespread, particularly in Europe and the United States.
By the early 1950s, endemic smallpox had been eradicated from Europe, the USSR, and North and Central America (see References: Fenner 1988: Chapter 5). Most of the outbreaks that occurred in Europe and North America after World War II were small and involved fewer than 50 cases (see References: Bhatnagar 2006). However, the disease remained endemic throughout most of the developing world, with an estimated 50 million cases occurring each year (see References: WHO: Fact sheet on smallpox).

Global Eradication of Smallpox

In 1959, the 12th World Health Assembly of the World Health Organization (WHO) passed the first resolution for global eradication of smallpox; however, it was not until 1967 that substantial resources were dedicated to the project.
The basic strategy of smallpox eradication included: (1) mass smallpox vaccination campaigns and (2) surveillance and containment of outbreaks.
After an extensive, sustained, international collaboration over a 12-year period, the International Commission for the Global Certification of Smallpox Eradication declared in December 1979 that smallpox had been globally eradicated (see References: Fenner 1988: Chapter 27).
The last reported case of endemic smallpox occurred in Somalia in 1977, and the last case human case, which involved accidental laboratory exposure, occurred in Birmingham, England, in 1978 (see References: CDC: Laboratory associated smallpox—England; CDC: Smallpox surveillance—worldwide).
The following epidemiologic features of smallpox facilitated global eradication (see References: Fenner 1988: Chapter 4):

Humans are the only natural reservoir for variola virus.
Vectorborne transmission of the virus does not occur.
The virus does not survive in nature for prolonged periods of time.
The full-blown clinical illness is easily recognizable, allowing for accurate clinical surveillance of the disease.
The infectivity of variola virus is relatively low (ie, transmission generally requires relatively close face-to-face contact except in uncommon circumstances), making it possible to effectively interrupt chains of transmission.
Generally, only persons who develop the characteristic rash illness transmit the virus; subclinical illness is rare and transmission from subclinical cases is not of epidemiologic importance.
No chronic carrier state of the virus occurs.
An effective vaccine exists.
The incubation period (ie, 10 to 12 days) is long enough for a vaccination/containment strategy to be effective.

Epidemiology

Reservoir

Before global eradication, the only reservoir for variola virus was humans. No natural reservoir for the virus currently exists.
Stocks of variola virus have been retained in two WHO-approved collaborating centers: the Centers for Disease Control and Prevention (CDC) in Atlanta and the Russian State Centre for Research on Virology and Biotechnology, Koltsovo, Novosibirsk Region, Russian Federation) (see References: WHO 2001).
There are concerns that not all the smallpox preparations developed in the Russian bioweapons program can be accounted for and that unknown caches of variola virus may exist (see References: Henderson 1998).

Environmental survival

Survival in the environment appears to be inversely proportional to temperature and humidity. In the pre-eradication era, smallpox had a higher incidence in the winter and spring in those climates where these seasons had low temperature and humidity.
Variola virus has been shown to remain stable for 2 to 4 months in scab material from smallpox patients (see References: MacCallum 1957).
Variola virus apparently can persist on fomites (such as linen and clothing) for extended periods of time (months to possibly years) (see References: Henderson 1999).
Vaccinia virus released as an aerosol is almost completely destroyed in an atmosphere of high temperature (31°C to 33°C) and humidity (80%). In cooler temperatures and lower humidity, vaccinia virus aerosol survives as long as 24 hours (see References: Henderson 1999). A recent study has shown that vaccinia virus is susceptible to germicidal ultraviolet light and that susceptibility increased with decreasing relative humidity (see References: McDevitt 2007). Variola virus is presumed to behave in a similar fashion.
Studies with vaccinia virus suggest that the virus can survive on selected food and environmental surfaces as long as 2 weeks and in water at 4.5ºC as long as 166 days (see References: Essbauer 2007). Although comparable data are not available for variola virus, the authors postulate that other orthopoxviruses may behave similarly to vaccinia virus.

Modes of transmission

Variola virus is predominantly transmitted person-to-person via inhalation of droplet nuclei (see References: Fenner 1988: Chapter 4). Transmission occurs most commonly among those with close face-to-face contact with an infected patient (particularly household contacts, since patients are usually ill enough to be confined to bed during the period of infectiousness).
Airborne transmission has been documented in two outbreaks that occurred in hospitals in the Federal Republic of Germany (one in 1961 and one in 1970) (see References: Wehrle 1970).

In the first outbreak, the index patient transmitted the virus to 19 persons, 10 of whom had no direct contact with the patient. The index patient had severe confluent skin involvement, ulcerative pharyngitis, and a barking cough.
In the second outbreak, the index patient transmitted the virus to 17 persons, none of whom had direct contact with the patient. The index patient had severe confluent skin lesions, severe bronchitis, and cough. Investigators noted that the relative humidity in the hospital was low (which may have facilitated survival of the virus) and that the design of the hospital set up strong air currents throughout the building (which may have facilitated dissemination of viral particles).

Fomite transmission (eg, from laundry and bedding) has been reported (see References: Dixon 1962, Kiang 2003). Contaminated fomites (ie, blankets) were used for intentional transmission of smallpox during the French-Indian wars in the United States in the 1700s (see References: Stearn 1945).
Transmission via direct contact with skin lesions and infected body fluids also has been recognized (see References: Kiang 2003).

Communicability

The infectious dose is presumed to be low (10 to 100 organisms) (see References: Franz 1997).
Most epidemiologic data suggested that infectiousness in smallpox correlated with rash onset, with patients in the prodromal phase generally not considered infectious (see References: Henderson: Smallpox as a biological weapon). This is distinct from varicella infection (ie, chickenpox), in which patients are infectious before rash onset. However, patients with smallpox should be considered infectious from the time of onset of fever, because virus is present in, and shed from, the oral lesions as they ulcerate during the 1 to 2 days of fever preceding rash onset (see References: CDC: Smallpox response plan and guidelines: Guide A; Breman 2002).
Infectiousness is considered to be highest during the first week after rash onset when lesions in the mouth ulcerate and release large amounts of virus into the saliva. Frequency of secondary transmission has been estimated (using a likelihood-based estimation procedure) as being highest between 3 and 6 days after onset of fever (see References: Nishiura 2007).
The observed secondary attack rates among unvaccinated close contacts have varied from 37% to more than 88% (see References: Arnt 1972, Heiner 1971, Kiang 2003, Rao 1968). The quantity of virus excreted in oropharyngeal secretions, the number of face-to-face contacts, and the extent of face-to-face exposure are considered key factors in determining infectiousness (see References: Kiang 2003).
The average number of cases infected by a primary case is estimated at 3.5 to 6 (see References: Gani 2001). This observation was consistent across analyses of outbreaks in isolated pre–20th century populations and in 30 outbreaks in 20th-century Europe. In these settings, herd immunity was low. This estimate suggests that in populations with little herd immunity, the transmission potential of smallpox would produce a rapid rise in outbreak cases before control measures could be applied.
The period of communicability lasts until all the lesions have scabbed over and the scabs have fallen off. Viable viral particles can be detected in scabs (see References: Wolff 1968; Fenner 1988: Chapter 2); however, scabs are considered relatively noninfectious, since the viral particles are bound in the fibrin matrix of the scab.

Use of Smallpox as a Biological Weapon

Historical perspective

Smallpox was used as a biological weapon during the French-Indian wars in the United States (1754-1767), when British soldiers gave the Indians blankets that had been used by smallpox patients (see References: Stearn 1945).
In 1972, more than 140 countries signed the Biological and Toxin Weapons Convention, which called for termination of all offensive biological weapons research and development and destruction of existing biological weapons stocks.
Despite participating in the 1972 convention, the former Soviet Union continued to expand its biological-weapons program throughout the 1980s and early 1990s. During that time, the Soviet Union reportedly developed weaponized variola virus that could be mounted in intercontinental ballistic missiles and bombs for strategic use (see References: Alibek 1999). A recent report from the Center for Nonproliferation Studies suggests that a 1971 outbreak of smallpox in Kazakhstan involving 10 people (three of whom died) may have resulted from an open-air test of a Soviet smallpox biological weapon on Vozrozhdeniye Island in the Aral Sea (a top-secret Soviet bioweapons testing site) (see References: Tucker 2002).
Currently, variola virus is known to be stored in two facilities (at the CDC in Atlanta and at the Russian State Centre for Research on Virology and Biotechnology, Koltsovo, Novosibirsk Region, Russian Federation).
In the early 1980s, WHO recommended that all existing stocks of variola virus held in other countries be either destroyed or shipped to one of the two WHO-approved collaborating centers. All countries reported compliance; however, there has been no systematic way to assure that all countries actually did comply with the WHO recommendations (see References: Henderson 2001). Also, there is no way to be certain that the virus has not fallen into the hands of rogue nations or potential terrorists (see References: Henderson 1998).
On several occasions, WHO has recommended that the remaining stores of variola virus be destroyed. However, in December 2001, the WHO Advisory Committee on Variola Virus Research recommended that existing stocks of the virus be retained for the time being so that various research goals can be achieved. The World Health Assembly has continued to authorize specific research projects that utilize the stocks, while acknowledging destruction of the stocks as its eventual goal (see References: WHO 2001, WHO 2005).

Impact of a smallpox release

Smallpox is of concern as a biological weapon for several reasons: much of the population is susceptible to infection, the virus carries a high rate of morbidity and mortality, vaccine is not yet available for general use, and past experience has demonstrated that introduction of the virus creates a great deal of havoc and panic (see References: Henderson 1998, O'Toole 2002).
Aerosol release of virus (such as into an airport or subway system) would be the most efficient form of release and would likely result in the highest number of cases. Other possibilities include use of "human vectors" (ie, persons who have been deliberately infected with smallpox) and use of fomites (eg, contamination of letters sent through the mail) (see References: Kiang 2003).
Several studies have used modeling to examine the impact of a deliberate release of smallpox virus. In a recent stochastic model, investigators estimated that 100 index smallpox cases in a city of 2 million would result in 730 additional cases, assuming that control measures begin at 25 days after release and that the outbreak is controlled with ring vaccination and case isolation (see References: Viboud 2003). Given the recent attention to smallpox, ongoing global vigilance to rapidly detect any recurrence through accidental or intentional release is necessary (see References: Breman 2003). Furthermore, even if all stocks of naturally occurring smallpox virus are destroyed, it is now possible to genetically engineer a similar viral agent in the laboratory setting. This capability requires that the medical and public health communities maintain smallpox preparedness into the foreseeable future (see References: Bray 2004).
A recent study suggested that donated blood could be screened using real-time polymerase chain reaction (PCR) methods to prevent the spread of variola virus through blood supplies, should it be introduced by an act of bioterrorism. In an experimental setting, the procedure (RealArt Orthopox LC PCR kit) demonstrated 100% specificity and sensitivity of 1,590 copies/mL for vaccinia in positive controls (see References: Schmidt 2005).

Government Oversight

The Intelligence Reform and Terrorism Prevention Act, designed to improve efforts to fight terrorism, was signed into law on Dec 17, 2004 (see References: Enserink 2005; Congressional Reports 2004; HoR 2004: Report 108-796). The legislation contained an amendment ("variola amendment") inserted at the last minute that imposes severe penalties for attempts to engineer or synthesize the smallpox virus. The amendment defines smallpox virus as any virus that contains more than 85% of the gene sequence of variola major or variola minor (see References: HoR 2004: Report 108-796, Title VI: Terrorism prevention). Penalties include fines of up to $2 million and prison terms ranging from 25 years to life) (see References: Enserink 2005; HoR 2004: Report 108-796).
The National Science Advisory Board for Biosecurity (NSABB) developed a framework in July 2007 to prevent misuse of research information, such as information on variola virus (see References: NSABB 2007).

Clinical Features of Variola Major

Variola major can be further classified into five clinical types on the basis of differences in rash characteristics and density; the prognosis differs among the types (see References: Fenner: Chapter 1). These are:

Ordinary smallpox
Flat-type (or malignant) smallpox
Hemorrhagic smallpox
Modified smallpox
Variola sine eruptione

In the pre-eradication era, diagnosing smallpox and distinguishing its type took into account clinical illness pattern, epidemiologic considerations, and laboratory findings. Although there is some overlap between ordinary, flat-type (or malignant) and hemorrhagic smallpox, their clinical and epidemiologic features are sufficiently distinct to warrant separate consideration (see below), particularly to enhance clinicians' awareness of the various clinical manifestations of what should be an extinct disease.

Modified smallpox was like ordinary smallpox but had an accelerated course and was a milder illness with fewer skin lesions and a low case-fatality rate; it was more likely to occur in persons with some immunity from past vaccination. Variola sine eruptione occurred in vaccinated contacts of cases and was characterized by sudden onset of fever, headache, and backache. Illness resolved in 1 to 2 days without development of a rash.

Case-fatality rates in the pre-eradication era for the various types of smallpox were high; however, such rates will be lower with modern medical management and intensive care.

Images of smallpox rashes are available from CDC (see References: CDC: Smallpox: images).

Ordinary Smallpox

Ordinary smallpox was the most common form of variola major infection and accounted for at least 90% of cases in the pre-eradication era.
The case-fatality rate was usually about 30% in unvaccinated persons (range, 15% to 45%) (see References: Fenner 1988: Chapter 1). Death resulted from hypotension and toxemia (associated with circulating immune complexes).
The rash illness of ordinary smallpox is somewhat similar to varicella, although disease severity is greater (see References: Henderson 1999: Smallpox: clinical and epidemiologic features).
The rash consists of firm, raised pustules and can be confluent, semiconfluent, or discrete.

Clinical features of ordinary smallpox are shown in the table below. A risk-evaluation algorithm can be found on the CDC Smallpox Web site to help clinicians determine if a patient with rash illness is at low or high risk of having smallpox on the basis of the clinical features of the illness (see References: CDC: Evaluate a rash illness suspicious for smallpox).

Clinical Features of Ordinary Smallpox
Feature	Characteristics
Incubation period^a	—10-13 days (usually about 12 days) —May be as short as 7 days and as long as 19 days
Prodrome	—Lasts 2-4 days —Frequency of prodromal symptoms in one large case series^b: ~Fever, 100% ~Chills, 60% ~Headache, 90% ~Backache, 90% ~Vomiting, 50% ~Pharyngitis, 15% ~Abdominal pain, 13% ~Diarrhea, 10%
Rash^a	—Enanthem on mucosa of mouth and pharynx usually begins about 24 hr before skin lesions appear (initially papular, then vesicular, then ulcerative over several days) —First few skin lesions often appear on face ("herald spots") —Lesions spread to trunk and proximal extremities and then to distal extremities —Lesions prominent on face and distal extremities, including palms and soles, in centrifugal pattern —Lesions initially maculopapular (days 1-2), then vesicular (days 3-5), then pustular (days 7-14); pustules gradually scab over by end of second week or during third week —Vesicular lesions often have central umbilication which may persist into pustular stage, but as lesions progress they gradually flatten —Pustules often described as "shotty" (ie, like hard, round foreign bodies embedded in skin) —Lesions extend deep into skin, often are painful, and pitted scarring occurs as they heal —Lesions may be discrete (relatively few in number), semiconfluent, or confluent —Lesions generally progress at same rate with relatively synchronous onset —In partially immune persons, clinical course may be much less severe and rash may be atypical with fewer lesions and more rapid healing (ie, "modified smallpox")
Laboratory features^a	—Relative or absolute increase in lymphocytes may be noted —Granulocytopenia may occur
Complications^b,c	—Massive amounts of subcutaneous fluid may accumulate during vesicular and pustular stages of rash, leading to severe fluid and electrolyte disturbances, including renal failure —Massive skin desquamation can occur in cases of confluent disease; patients may clinically and metabolically resemble severe burn victims —Viral bronchitis/pneumonitis occurs relatively commonly —Other less common complications: ~Corneal ulceration (about 1% of cases) and/or keratitis (about 0.25% of cases) (may cause corneal scarring and blindness) ~Secondary bacterial infections (particularly skin and pulmonary infections) ~Encephalitis (0.2% of cases) ~Osteomyelitis or arthritis (about 1.7% of cases; usually in children) ~Orchitis (rare, 0.1%)
Case-fatality rates^d	—Overall case-fatality rate for ordinary smallpox, 15%-45%^a —Likelihood of death varies by type of disease (ie, confluent, semiconfluent, or discrete)^c —Observed case-fatality rates by type of disease among unvaccinated patients in one large series^b: ~Overall rate, 30% ~Confluent disease, 62% ~Semiconfluent disease, 37% ~Discrete disease, 9%
^aSee References: Fenner 1988: Chapter 1. ^bSee References: Rao 1972. ^cSee References: Koplan 1979. ^dCase-fatality rates are based on historical data from pre-eradication era; such rates may be lower with modern medical management and intensive care.

Flat-Type (Malignant) Smallpox

Flat-type smallpox accounted for about 6% of cases in the pre-eradication era and occurred most commonly in children; illness was usually fatal.
The rash seen in flat-type smallpox involves flattened, confluent lesions rather than the characteristic firm pustules seen with ordinary smallpox.
Flat-type smallpox is thought to be associated with a deficient cellular immune response to the virus, although immunologic data are generally lacking (see References: Henderson 1999: Smallpox as a biological weapon).

Clinical features are shown in the table below.

Clinical Features of Flat-Type Smallpox
Feature	Characteristics
Incubation period	—Similar to ordinary smallpox (mean, 12 days; usual range, 10-14 days)
Prodrome	—Similar to ordinary smallpox (ie, fever, headache, backache, abdominal pain) —Lasts 2-4 days —Severe toxemia may occur
Rash illness^a,b	—Lesions develop slowly —Lesions rarely progress to pustular stage but remain soft and flattened —Lesions may be "velvety" to touch by 4th or 5th day —Lesions often confluent —Lesions and surrounding skin warm to the touch and tender to slight pressure —If patient survives, lesions gradually disappear without forming scabs and without scarring —Skin peeling or desquamation may occur as lesions heal
Laboratory features	—Similar to ordinary smallpox —Relative or absolute increase in lymphocytes may be noted —Granulocytopenia may occur
Case-fatality rate^c	—Case-fatality rate 97% in one series involving 236 patients^d
^aSee References: Fenner 1988: Chapter 1. ^bSee References: Dixon 1948. ^cCase-fatality rates are based on historical data from the pre-eradication era; such rates may be lower with modern medical management and intensive care. ^dSee References: Rao 1972.

Hemorrhagic Smallpox

Hemorrhagic smallpox was rare and accounted for between 2% and 3% of cases in the pre-eradication era. In one series, 200 cases occurred out of 6,942 hospitalized patients (see References: Rao 1972).
Illness was more common in adults, and pregnant women appeared to be at greater risk.
Hemorrhagic smallpox involved hemorrhages into the skin and/or mucous membranes. Early-onset and late-onset forms were described (see References: Fenner 1988: Chapter 1).
The pathologic features of hemorrhagic smallpox are consistent with disseminated intravascular coagulation (see References: Mitra 1976, Mehta 1967).
As with malignant smallpox, a defective immune response is suspected as the cause; however, immunologic data generally are lacking (see References: Henderson 1999: Smallpox as a biological weapon). Several studies have found lower antibody responses among patients with hemorrhagic disease compared with those with ordinary disease (see References: Sarkar 1967, Downie 1969).

Clinical features are outlined in the table below.

Clinical Features of Hemorrhagic Smallpox
Feature	Characteristics
Incubation period	—Similar to ordinary smallpox (mean, 12 days; usual range, 10-14 days).
Prodrome^a	—Early-onset form: illness onset sudden, with high fever, severe headache and backache, and toxemia; hemorrhages often noted by day 2 —Late-onset form: illness begins with a typical prodrome, lasting 3-4 days
Rash illness^a,b	—Early-onset form: generalized dusky erythema, petechiae, and ecchymoses occur soon after illness onset —Late-onset form: lesions begin as macules and develop into pustules; bleeding at base of skin lesions occurs
Hemorrhagic manifestations	—In both forms, bleeding may occur from mucosal surfaces —Features in one series of nine patients with early-onset form^c: ~Subconjunctival hemorrhage, 67% ~Hematuria, 56% ~Epistaxis, 33% ~Hematemesis and/or melena, 33% ~Hemoptysis, 33% ~Bleeding from gums, 33%
Laboratory features^c,d	—Relative or absolute increase in lymphocytes may be noted —Granulocytopenia may occur —Features consistent with disseminated intravascular coagulation are common: ~Thrombocytopenia ~Hypofibrinogenemia ~Clotting-factor deficiency ~Prolonged prothrombin time
Case-fatality rate^e	—In one series of 85 patients, case-fatality rate was 96%^b —Death usually occurs during the first week of illness
^aSee References: Fenner 1988: Chapter 1. ^bSee References: Rao 1972. ^cSee References: Mitra 1976. ^dSee References: Mehta 1967. ^eCase-fatality rates are based on historical data from pre-eradication era; such rates may be lower with modern medical management and intensive care.

Smallpox in Children

The clinical picture of smallpox in children generally is similar to that seen in adults. However, in one series of 100 cases among children in India, the frequency of various signs and symptoms varied somewhat from those classically described (see References: Sheth 1971). For example, headache and backache were less common, whereas vomiting, conjunctivitis, and cough were somewhat more common. Signs, symptoms, and complications identified in that series are shown in the table below. Of the 100 patients, 66 had confluent disease, 25 had discrete disease, six had flat-type smallpox, and three had hemorrhagic smallpox. Overall, 34 children died (including all of those with flat-type or hemorrhagic smallpox).

The case-fatality rate in infants may be somewhat higher than in older children or adults (ie, >40%) (see References: Fenner 1988: Chapter 1). In one case series, the case-fatality rate for infants was 85% (see References: Guha Mazumder 1975).

Infection in pregnant women often leads to premature labor and death of the fetus (see References: Fenner 1988: Chapter 1). The overall case-fatality rate for pregnant women estimated from analysis of mid-20th century outbreaks was calculated to be about 34.3%. The proportion of miscarriage or premature birth was found to be 39.9%, but no clear pattern was discernable. Premature birth was highest during the last trimester of pregnancy (see References: Nishiura 2006: Smallpox during pregnancy) No clear congenital syndrome has been associated with smallpox infection in utero.

Signs, Symptoms, and Complications of Smallpox in Children

Symptoms

Headache (15%)
Backache (15%)
Retro-orbital pain (15%)
Prostration (75%)

Signs

Fever (100%)
Vomiting (83%)
Conjunctivitis (77%)
Hepatosplenomegaly (75%)
Hypotonia (75%)
Cough (71%)
Hoarseness (71%)
Edema (71%)
Delirium (64%)
Convulsions (7%)

Complications

Constipation (66%)
Bronchopneumonia (37%)
Alopecia (19%)
Osteomyelitis (4%)
Subcutaneous abscess (3%)
Diarrhea (2%)

Adapted from Sheth 1971 (see References).

Clinical Features of Variola Minor

Variola minor is a milder form of smallpox that is caused by distinct strains of variola virus. Variola minor was first recognized in the late 1800s; during the early 20th century, it was the most prevalent form of smallpox in the United States and Great Britain. The illness may be difficult to distinguish from variola major infection in partially immune persons.

Distinguishing Features of Variola Major and Variola Minor
Feature	Variola Major	Variola Minor^a,b
Prodrome	—Constitutional symptoms severe	—Constitutional symptoms tend to be mild
Rash illness	—Lesions often confluent or semiconfluent —Rash evolves over 2-3 wk	—Lesions usually discrete —Rash evolves over 1-2 wk
Complications	—Flat-type or hemorrhagic disease occurs more commonly (6% and 2%, respectively, in one large series^c)	—Hemorrhagic disease rare (<0.5%)
Case-fatality rate	—May be high (15%-45%)	—Fatal outcomes rare (<1%)
^aSee References: Fenner 1988: Chapter 1. ^bSee References: Ker 1967, Marsden 1948. ^cSee References: Rao 1972.

Differential Diagnosis

Differential Diagnosis of the Rash illness

Other rash illnesses, outlined in the table below, are included in the differential diagnosis of smallpox.

Differential Diagnosis for Smallpox
Condition	Agent	Distinguishing features
Ordinary Smallpox^a
Chickenpox	VZV	See Distinguishing Features of Smallpox and Chickenpox below
Human monkeypox	Monkeypox virus	See Monkeypox below
Disseminated herpes zoster	VZV	—Usually occurs in immunocompromised hosts —Past history of chickenpox
Impetigo	Staphylococcus aureus Streptococcus pyogenes	—Lesions often pruritic and not painful —Lesions focal and not usually disseminated —Lesions not "shotty" —Gold-colored crusted plaques are classic —Lesions superficial and not embedded into dermis —Constitutional symptoms generally absent or minimal —Usually occurs in children
Hand, foot, and mouth disease	Coxsackievirus	—Usually occurs in children <10 yr of age —Has autumn seasonal pattern —Lesions may be confined to hands and feet (although dissemination may occur)
Disseminated herpes simplex	Herpes simplex virus	—Usually occurs in immunocompromised hosts —Lesions are vesicular and do not progress to pustules
Secondary syphilis	Treponema pallidum	—Rash generally does not include vesicular phase —Lesions not "shotty" —Constitutional symptoms relatively mild —Lesions generally evolve slowly from macules to papules to pustules (often over several weeks)
Molluscum contagiosum	Molluscipoxvirus	—Usually occurs in healthy children or HIV-positive adults —In healthy adults, lesions generally occur in genital area —Lesions are painless —Constitutional symptoms generally are absent —Lesions may persist for several months (or longer in immunocompromised patients)
Erythema multiforme major (including Stevens-Johnson syndrome)	Associated with various infectious and noninfectious processes	—Constitutional symptoms and rash usually appear at same time —Rash evolves rapidly —Bullae or "bull's-eye" lesions common —Extensive mucous membrane involvement, including conjunctivitis, common
Drug eruptions	Noninfectious	—Lesions generally not pustular —History of drug exposure —Fever may be present, but severe toxemia usually absent
Bullous pemphigoid	Noninfectious	—Tense bullae characteristic —Occurs most commonly in elderly —Intense pruritis may be present —Constitutional symptoms usually absent —Peripheral eosinophilia may be noted
Other skin conditions	Noninfectious	—Acne —Insect bites —Contact dermatitis
Hemorrhagic Smallpox
Meningococcemia	Neisseria meningitidis	Rapid progression to shock and often death
Hemorrhagic varicella	VZV	Usually occurs in immunocompromised children
Rocky mountain spotted fever	Rickettsia rickettsii	—Tick exposure history may be obtained —Occurs April through May —Most US cases occur in southeastern and south-central states
Ehrlichiosis	Ehrlichia chaffeensis Erhlichia phagocytophilia	—Tick exposure history may be obtained —Petechial rash uncommon —Peripheral blood smear may show morulae in neutrophils of patients with human granulocytic ehrlichiosis
Septicemia caused by gram-negative bacteria	Various bacterial agents	—Underlying illness usually present
Abbreviation: VZV, varicella-zoster virus. ^aOther rash illnesses (eg, measles, rubella, scabies, scarlet fever) also may be considered in the differential diagnosis, although the rashes caused by these conditions generally are not characteristic of smallpox. Adapted from Fenner 1988: Chapter 1; CDC: Acute, generalized vesicular or pustular rash illness protocol; Moore 2006 (see References).

Monkeypox

Historical perspective in Africa

Human monkeypox is caused by monkeypox virus, which, like variola virus, is in the Orthopoxvirus genus. Monkeypox is similar to smallpox, but illness is generally milder. Recognized cases have occurred predominantly in Western and Central Africa. Pertinent historic information about monkeypox in Africa is as follows:

The illness in humans is similar to discrete or semiconfluent ordinary smallpox (see References: Jezek 1987). A prodrome (fever, headache, backache) lasting 1 to 3 days occurs, followed by eruption of a smallpox-like rash that lasts 2 to 4 weeks.
Monkeypox cases tend to have prominent lymphadenopathy, which generally is not a feature of either chickenpox or smallpox (see References: Arita 1985, Breman 1980, Jezek 1987). This can be an important distinguishing characteristic between the three conditions.
The first human case was recognized in 1970; since then, sporadic cases and outbreaks have been recognized in Africa, although the illness appears to be relatively uncommon.
Natural animal reservoirs in Africa include several squirrel species and forest-dwelling primates (see References: Khodakevich 1988). Lagomorphs (rabbits) and other rodents including prairie dogs, also appear to be susceptible to infection. The ecological requirements and geographic distributions have been identified, and these may support further field studies and guide public health intervention strategies (see References: Levine 2007).
The case-fatality rate was 11% in one series of 282 patients (see References: Jezek 1987) and was 3% in one outbreak involving 71 cases (see References: CDC: Human monkeypox), suggesting that the illness is less severe than smallpox. In both investigations, all deaths occurred in children less than 10 years of age (who had not received earlier smallpox vaccination).
Person-to-person transmission has been demonstrated (see References: Arita 1985; Breman 1980; CDC: Human monkeypox; Jezek 1986; Jezek 1988). Secondary attack rates of 7.2%, 7.5%, and 15% have been reported among household contacts who had not received prior smallpox vaccination (see References: Arita 1985, Jezek 1986, Jezek 1988). These secondary attack rates are lower than those observed for smallpox and reflect the lower propensity for spread of monkeypox compared with smallpox.

US 2003 outbreak

In June 2003, an outbreak of monkeypox was recognized in the Midwestern United States (see References: CDC: Multistate outbreak of monkeypox—Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin, 2003; Reed 2004). Key findings from the outbreak are as follows:

Seventy-one cases were reported to CDC; 18 (26%) patients were hospitalized but no fatalities occurred.
No exposed healthcare workers developed monkeypox symptoms, although one worker had serologic evidence of recent orthopoxvirus infection; that person had received smallpox vaccine during the previous year (see References: Fleischauer 2005).
Thirty exposed persons received smallpox vaccine to prevent monkeypox; three reported rash within 2 weeks after vaccination and one of these persons was confirmed as having monkeypox.
In one report, three exposed persons were identified who had no symptoms but had serologic evidence of recent monkeypox infection. All three had received smallpox vaccine in the past (13, 29, and 48 years earlier). These findings suggest long-term persistence of cross-protective immunity to orthopoxvirus infection following smallpox vaccination in these individuals (see References: Hammarlund 2005).
The outbreak was traced to contact with infected prairie dogs; the prairie dogs became infected through contact with six species of African rodents (including Gambian giant rats, rope squirrels, tree squirrels, brushtail porcupines, striped mice, and dormice).
In November 2003, the Food and Drug Administration (FDA) and CDC issued an interim final rule prohibiting importation of rodents from Africa, including species responsible for the monkeypox outbreak (see References: FDA/CDC 2003: Control of communicable diseases; restrictions on African rodents, prairie dogs, and certain other animals). In addition, the rule established or modified restrictions on the import, capture, transport, sale, barter, exchange, distribution, and release of prairie dogs and implicated species of African rodents.
A risk assessment from the FDA has concluded that the potential for new domestically acquired human cases is low; however, if the disease were to become established domestically via escaped or illegally bred animals, the disorder could have substantial public health impact (see References: Bernard 2006).
CDC has published guidance for autopsy and safe handling of human remains of monkeypox patients (see References: CDC 2003: Interim guidance for autopsy and safe handling).

Distinguishing Features Between Smallpox, Monkeypox, and Chickenpox

Smallpox and monkeypox are generally quite similar, although smallpox often is more severe and the case-fatality rate is higher. Early in the clinical course, smallpox or monkeypox may be mistaken for chickenpox if the clinical suspicion for orthopoxvirus infection is low. Also, smallpox in partially immune patients may be mild and may resemble chickenpox. An assessment of suspected smallpox cases referred to CDC between 2002 and 2004 found that chickenpox accounted for more than half of the cases (see References: Seward 2004). Distinguishing features of the three illnesses are outlined in the table below.

Distinguishing Features Between Smallpox, Chickenpox, and Monkeypox
Feature	Smallpox (Variola Major)^a	Chickenpox	Monkeypox
Prodrome^b	Lasts 2-4 days, with high fever, headache, backache, severe prostration; vomiting and severe abdominal pain may occur	Prodrome often absent; if present, it is mild and brief (ie, about 1 day)	Lasts about 2 days and is similar to that seen with smallpox
Distribution of rash	Begins on oral mucosa, spreads to face, then expands in centrifugal pattern (ie, most dense on face and distal extremities)	Begins on trunk and expands in centripetal pattern (ie, most dense on trunk)	Often begins on face and spreads in centrifugal pattern (although cases have been reported with centripetal pattern of spread)
Lesions on palms and soles	Common	Almost never occur	Common
Lymphadenopathy	Rare	Rare	Common (up to 90%)
Timing for occurrence of lesions	Generally emerge over 1-2 days and then progress at same rate	Occur in "crops" and may be at different stages of maturation at any given point in time	Lesions usually progress at same rate but may occur in crops (in about 20% of patients)
Evolution of lesions	Progress over several days from macules (day 1), to papules (day 2), to vesicles (days 3-5), to pustules (days 7 to about 14), to scabs (day 14 to about 20)	Progress quickly over about 24 hr from macules to papules to vesicles, then to crusted lesions	Progress in pattern similar to smallpox
Sensation associated with lesions	May be painful and only become pruritic during scabbing stage	Often intensely pruritic; not usually painful unless superimposed bacterial infection occurs	May be painful (although often milder than smallpox)
Depth of lesions	Extend deep into dermis and often cause pitted scarring	Superficial and generally do not cause scarring	Generally superficial (although pitted scarring can occur)
Duration of illness	14-21 days	4-7 days	14-21 days
Severity	Patients often appear toxic and case-fatality rate may be as high as 50%	Patients often do not appear severely ill and illness is rarely fatal	Illness can vary in severity but often is mild and self-limited
Epidemiology	Cases can be expected to occur in all age-groups; illness may be somewhat milder in adults over age 30 who were vaccinated as young children	Most cases occur in children; adults likely to be immune	Cases can be expected to occur in all age-groups; illness may be milder in people who have received smallpox vaccination
^aIllness may be milder in patients with partial immunity; fever may be less common and fewer lesions may occur with more rapid healing. ^bAlthough the prodrome may be milder in patients with chickenpox, a review of 932 chickenpox cases demonstrated that 7% to 17% of unvaccinated patients with chickenpox may meet the smallpox febrile prodrome criteria as put forth by CDC (see References: Moore 2004). Adapted from CDC: Acute, generalized vesicular or pustular rash illness protocol and Giulio 2004 (see References).

Determining the Likelihood of a Smallpox Diagnosis

The likelihood of a smallpox diagnosis determines the appropriate laboratory testing and handling of specimens. CDC has developed criteria for determining the risk of smallpox (see References: CDC: Acute, generalized vesicular or pustular rash illness protocol).

High risk for smallpox (when all three of the following features are present):

Febrile prodrome (occurring 1 to 4 days before rash onset) with fever greater than 102°F and at least one of the following:

Prostration
Headache
Backache
Chills
Vomiting
Severe abdominal pain

Classic smallpox lesions:

Deeply embedded in the dermis
Firm/hard
Round
Well-circumscribed
May be umbilicated
May be discrete, semiconfluent, or confluent

Lesions in the same stage of development (ie, on any one area of the body, all of the lesions are at the same stage [all lesions are papules or vesicles or pustules])

Moderate risk for smallpox:

Febrile prodrome (as outlined above under "High risk for smallpox") and at least one major smallpox criteria (classic smallpox lesions as described above or lesions in the same stage of development) or
Febrile prodrome and at least four of the five minor criteria:

Centrifugal distribution (lesions are more numerous on the face and distal extremities)
First lesions appeared on the oral mucosa/palate, face, or forearms
Patient appears toxic or moribund
Slow evolution of lesions from macules to papules to pustules over several days
Lesions on the palms and soles

Low risk for smallpox:

No viral prodrome or
Febrile prodrome and fewer than four of the five minor criteria outlined above (under "Moderate risk for smallpox")

A recent study indicated that physicians in the United States may be poorly prepared to diagnose smallpox. Only 36% of 178 physicians correctly answered 3 of 4 questions regarding smallpox and chickenpox differential diagnosis. In addition, only 17% indicated that they felt "comfortable" diagnosing smallpox and 95% thought physicians needed more training in smallpox diagnosis (see References: Woods 2005). Similarly, baseline knowledge assessment of 631 physicians in 30 internal medicine residency programs in 16 states and Washington, DC, showed that only 50.7% of participating physicians could correctly diagnose smallpox (see References: Cosgrove 2005).

An algorithm developed by the CDC after the 2001 bioterrorism attack to rapidly evaluate patients for smallpox may prove useful. A recent prospective, multicenter study used the algorithm to classify 26,747 cases of rash or rashlike illness at emergency departments and inpatient units of 12 acute-care hospitals in six states. Eighty-nine patients presenting with acute generalized vesicular or pustular rash were determined to be eligible for the study, and 73 were enrolled. Physicians or study staff classified none of the 73 as being at high risk, 72 as low risk, and 1 as moderate risk of having smallpox. The discharge diagnosis for 55 of the 73 patients was varicella illness. Use of the algorithm did not result in misclassification of any patients as high risk for smallpox (see References: Hutchins 2008).

Laboratory Diagnosis

Specimen Collection and Handling

The CDC has established algorithms for laboratory evaluation of patients with acute, generalized vesicular or pustular rash illnesses, based primarily on likelihood of smallpox (see References: CDC: Acute, generalized vesicular or pustular rash illness testing protocol in the United States).

High risk for smallpox (see Criteria for Determining the Likelihood of Smallpox): Contact public health authorities immediately, before collecting specimens. Photograph patient's clinical presentation for uploading to public health departments and CDC (use digital camera or scan film image). Initial testing will be performed by Laboratory Response Network (LRN) variola surge capacity laboratories in parallel with the CDC. Electron microscopy (EM) can be performed at the local facility, assuming BSL-3 containment is used for preparation of the grid. Variola virus should be ruled out prior to other testing, and results should not be released without CDC confirmation. The Federal Bureau of Investigation may initiate chain-of-custody for high-risk specimens.
Low or moderate risk for smallpox (see Criteria for Determining the Likelihood of Smallpox): Testing may be conducted at LRN laboratories and/or clinical laboratories with at least BSL-2 facilities. Testing for suspected cases of monkeypox or adverse vaccine reactions should be conducted at LRN laboratories. If varicella-zoster virus (VZV) diagnosis is questionable, laboratory testing should begin as soon as possible. Testing options include Tsank smear; direct fluorescent antibody test for VZV and herpes simplex virus (HSV); polymerase chain reaction (PCR) for VZV, HSV, and enterovirus; EM; and viral culture. If all results are negative, nonvariola orthopox infection, such as a vaccine-related reaction or monkeypox infection should be considered. Contact the local LRN laboratory for testing. If nonvariola orthopox tests also are negative, reevaluate the patient and assess the need for additional dermatologic and histologic testing. If upon reevaluation the risk for smallpox is upgraded to high, switch to the high-risk protocol and contact local public health authorities.
Environmental samples: Testing of environmental samples is performed only at LRN reference laboratories under the direction of public health or public safety authorities.
It is likely that laboratories will receive specimens from patients with possible orthopoxvirus infections without being notified of risk level for smallpox. Theoretically, properly practiced universal precautions should protect the laboratory worker and community from accidental exposure.

Specimen Collection

If a patient is defined as high risk for smallpox (see Determining the Likelihood of a Smallpox Diagnosis above), physicians should immediately contact their local or state health department for further instructions before collecting specimens.
CDC has outlined procedures for collecting specimens from patients who may have smallpox (see References: CDC: Smallpox response plan and guidelines: Guide D).
Only recently vaccinated (ie, within the past 3 years) personnel wearing appropriate barrier protection (ie, gloves, gown, shoe covers) should be involved in specimen collection.
If unvaccinated personnel must collect specimens, they should wear fit-tested N95 respirators and appropriate barrier protection. They also should have no contraindications to vaccination in case the diagnosis of smallpox is confirmed and vaccination is immediately required.

The following table outlines collection of laboratory specimens for the diagnosis of smallpox (variola) and smallpox vaccine (vaccinia)–associated infections.

Collection of Laboratory Specimens for the Diagnosis of Smallpox (Variola) and Smallpox Vaccine Virus Infection (Vaccinia)
Sample	Specimen Collection^a
Vesicles or pustules	—Sanitize the patient's skin with an alcohol wipe and allow to dry. —Use scalpel (or 26-gauge needle) to open and remove top of vesicle or pustule; place skin of vesicle top into a 1.5- to 2-mL screw-capped or plastic tube, let dry. —Scrape base of vesicle or pustule with blunt edge of scalpel or with wooden end of applicator stick or swab and smear scrapings onto glass or plastic light microscope slide. Allow to air dry for 10 min. —Take another slide and touch it repetitively to open lesion using progressive movement of slide to make a touch prep. Allow to air dry 10 min. —Store dried slides in plastic slide holders, using a different holder for each patient. —If slide is not available, swab base of lesion with polyester or cotton swab, place in screw-capped plastic vial, break off applicator handle, and screw on lid (do not add transport medium to vial). —If available, touch shiny side of 3 electron microscope grids to unroofed base of lesion and air dry; place in gridbox. Use varying degrees of pressure (minimal, light, and moderately firm) in application of each grid to unroofed lesion. —Biopsy two vesicles with 3.5- or 4-mm punch biopsy kit; place one biopsy in formalin and one in 1.5- to 2-mL screw-capped container without added fluid. —Draw 10 cc blood into plastic marble-topped tube or plastic yellow-topped serum separator tube; if plastic tubes not available, use equivalent glass tubes and package with styrofoam protector (Note: central line sample may be needed if peripheral blood draw is difficult because of sloughing skin in dense rash area). —Swab or brush posterior tonsillar tissue and package in 1.5- to 2-mL tube, as above (do not add transport medium). —Draw 5 cc blood into plastic purple-topped tube, gently shake tube to mix contents (if plastic not available, use glass as described above)
Scab lesions	—Sanitize patient's skin with alcohol wipe and allow to dry. —Use 26-gauge needle to pry off at least four scabs. —Place two scabs in each of two screw-capped plastic 1.5- to 2-mL vials. —Obtain two biopsy specimens with a 3.5- or 4-mm punch biopsy kit; place one in formalin and one in 1.5- to 2-mL screw-capped container. —Draw 10 cc blood into plastic marble-topped tube or plastic yellow-topped serum separator tube as described above. —Collect swab of tonsillar tissue as described above. —Draw 5 cc blood into plastic purple-topped tube as described above.
Nondermatologic specimens	Collect as appropriate, such as cerebrospinal fluid for post–vaccinia vaccine encephalitis.
Autopsy specimens	—Ship frozen portions of skin-containing lesions, liver, spleen, lung, lymph nodes, and/or kidney. —Collect formalin-fixed tissue from skin-containing lesions, liver, spleen, lung, lymph nodes, and/or kidney; package separately from frozen fresh tissue. —Use plastic vials, bottles, or slide holders as primary container for all specimens.
^aCheck with local LRN laboratory before collecting specimens. Specific collection recommendations change and may vary depending on local policies. Adapted from CDC: Smallpox response plan and guidelines: Guide D; CDC: Specimen collection of smallpox (vaccinia) vaccine virus; CDC: Current expectations for laboratory testing and adverse smallpox vaccine reactions; CDC: Laboratory Information > Specimen Selection; CDC: Smallpox and vaccinia laboratory testing: a national training initiative (see References).

Handling and shipping

Storage and shipping conditions (see References CDC: Smallpox response plan and guidelines: Guide D; CDC: Specimen collection of smallpox [vaccinia] vaccine virus; CDC: Current expectations for laboratory testing and adverse smallpox vaccine reactions; CDC: Laboratory Information > Specimen Selection; CDC: Smallpox and vaccinia laboratory testing: a national training initiative):

For patients with high risk of smallpox, contact public health authorities before collecting, processing, or shipping specimens.
Keep all specimens away from direct sunlight.
For formalin-fixed specimens, electron microscope grids, and touch preparations, store and ship at room temperature.
For whole blood and other specimens shipped within 24 hours of collection, store and ship refrigerated (4^ºC). (Note: Spin, separate, and freeze serum onsite if shipping is to be delayed.)
For serum and fresh biopsy material and other material potentially containing infectious particles if shipped more than 24 hours after collection, store and ship on dry ice (–20^ºC to –70^ºC).
Seal vials with parafilm to avoid pH changes from dry-ice vapors.

Packaging:

Package one sample per container.

Additional shipping information:

Guidelines have been published for packing and shipping of infectious substances, diagnostic specimens, and biological agents from suspected bioterrorism (see References: ASM: Sentinel laboratory guidelines for suspected agents of bioterrorism: packing and shipping infectious substances, diagnostic specimens, and biological agents). Variola virus is classified under WHO risk group 4. In general, specimens or culture isolates that are reasonably suspected to contain variola virus must be transported as "infectious substances." International Air Transport Association (IATA) rules require training of all individuals involved in the transport of dangerous goods, including infectious substances.

Laboratory Response Network (LRN)

The LRN is a national network of approximately 150 laboratories. The network includes the following types of labs: federal, state, and local public health, military, food testing, environmental, veterinary, and international (located in Canada, the United Kingdom, and Australia) (see References: CDC: Facts about the Laboratory Response Network).

The LRN structure for bioterrorism designates laboratories as either national, reference, or sentinel. Designation depends on the types of tests a laboratory can perform and how it handles infectious agents to protect workers and the public.

National laboratories have unique resources to handle highly infectious agents and the ability to identify specific agent strains.
Reference laboratories, sometimes referred to as "confirmatory reference," can perform tests to detect and confirm the presence of a threat agent. These laboratories ensure a timely local response in the event of a terrorist incident. Rather than having to rely on confirmation from laboratories at the CDC, reference laboratories are capable of producing conclusive results; this allows local authorities to respond quickly to emergencies. These are mostly state or local public health laboratories with BSL-3 containment facilities that have been given access to nonpublic testing protocols and reagents.
Sentinel laboratories represent the thousands of hospital-based labs that are on the front lines. Sentinel laboratories have direct contact with patients. In an unannounced or covert terrorist attack, patients provide specimens during routine patient care. Sentinel laboratories could be the first facility to spot a suspicious specimen. A sentinel laboratory's responsibility is to refer a suspicious sample to the right reference laboratory. These laboratories generally have at least BSL-2 containment.
LRN variola surge capacity laboratories are facilities selected by the CDC to conduct enhanced variola virus identification tests and handling procedures (see References: CDC: Acute, generalized vesicular or pustular rash illness testing protocol in the United States).
Laboratory safety practices associated with variola virus and other potential agents of bioterrorism have been reviewed elsewhere (see References: Sewell 2003; CDC: Laboratory Information > Microbiology Biosafety).
Vaccination is not recommended for LRN sentinel laboratory personnel (see References: CDC: Laboratory Information > Vaccines). If a sample containing suspect smallpox virus is handled, vaccination within 3 days postexposure is considered effective.
Variola major virus (smallpox virus), variola minor virus (alastrim), and monkeypox virus are classified as select agents and therefore are regulated under 42 CFR part 73, which was published as a Final Rule in the Federal Register in 2005 (see References: HHS 2005: Possession, use, and transfer of select agents and toxins). As specified in the Public Health Security and Bioterrorism Preparedness and Response Act of 2002, 42 CFR part 73 provides requirements for laboratories that handle select agents (including registration, security risk assessments, safety plans, security plans, emergency response plans, training, transfers, record keeping, inspections, and notifications). For more information about CDC’s Select Agent Program, see References: CDC: Select agent program. In addition, CDC has published additional guidelines for enhancing laboratory security for laboratories working with select agents (see References: CDC: Laboratory security and emergency response guidance for laboratories working with select agents).

Tests for Detection and Identification of Variola Virus

Culture on egg chorioallantoic membrane (CA): This is the classical method for identification of poxviruses and was used extensively before the eradication of smallpox. Poxviruses grow on CA, and each species forms characteristic pock lesions under defined temperature conditions (see References: Fenner 1988: Chapter 2). CA requires BSL-4 isolation.
Direct examination of vesicle or pustular material: As one of the largest viruses known, variola virus and aggregations of virus (Guarnieri bodies) may be seen in the cytoplasm of Giemsa-, hematoxylin-eosin (H-E)-, or silver-stained preparations viewed by light microscopy. Guarnieri bodies appear reddish purple with Giemsa stain and hematoxylino-eosinophilic with Bouin-fixed H-E, they contain Feulgen-positive material, and they show no evidence of fat or polysaccharide on histochemical examination (see References: Kato 1959). Direct examination was used in the past in outbreak settings and would likely be useful if smallpox were reintroduced. It is not considered reliable today as an identification or detection tool because of difficulty of interpretation (see References: Fenner 1988: Chapter 2).
Tissue culture: Growth in cultured cells has been used for quantitative culture of variola virus, and attempts have been made to characterize its cytopathic effect for identification purposes (see References: Marennikova 1974, Fenner 1988). As with direct examination by light microscopy, this is important because current tissue culture methods may result in inadvertent discovery. The cytopathic effect of variola virus is not considered a reliable method for identification of the virus (see Inadvertent Discovery of Variola Virus in a Laboratory Specimen below).
EM: Negative staining is used to visualize the characteristic large brick shape and fine structure detail of poxviruses (see References: CDC: Smallpox vaccination laboratory support; Madeley 2003). In the past, EM was found to be successful at detection and general differentiation of viral particles in approximately 95% of patients with variola or monkeypox infections and 65% of patients with vaccinia infections. EM played an important role in the 2003 US monkeypox outbreak. A protocol is available online (see References: CDC: Negative staining electron microscopic protocol for rash illness). Several characteristics of EM should be kept in mind:

Relatively rapid
Can distinguish orthopoxviruses from other viral agents
Cannot differentiate between variola and vaccinia viruses
May not be as sensitive as PCR-based methods

PCR-based methods

PCR now plays a significant role in the rash-illness testing algorithm (see References: CDC: Acute, generalized vesicular or pustular rash illness testing protocol in the United States). However, because the worldwide prevalence of variola infection is zero, the positive predictive value (PPV) of variola-specific PCR testing approaches zero if applied to cases that do not meet the CDC case definition for high risk of smallpox. Such testing is not recommended pre-event because of the potential serious consequences of false-positive results. The use of multiple methods and multiple specimens increases the cumulative PPV of laboratory testing (see References: CDC: Smallpox and vaccinia laboratory testing: a national training initiative).
LRN assays

A real-time PCR method based on the DNA polymerase E9L gene has been developed, validated, and deployed for vaccinia virus. This assay will also detect cowpox virus and monkeypox virus. In North America a positive test is considered diagnostic for vaccinia virus unless medical or epidemiologic evidence suggests otherwise. With slight modifications to the fluorescently labeled probe, this assay can also be used to detect variola virus (see References: CDC: Smallpox and vaccinia laboratory testing: a national training initiative).
A generic orthopoxvirus assay that utilizes a conserved target is being used at LRN laboratories for use as a screening test (see References: CDC: Smallpox and vaccinia laboratory testing: a national training initiative; CDC: Acute, generalized vesicular or pustular rash illness testing protocol in the United States).

Other PCR-based assays

A variety of additional PCR-based assays have been developed for detection of orthopoxviruses (see References: Aitichou 2008, Kulesh 2004, Olson 2004, Pulford 2004, Scaramozzino 2007, Sofi Ibrahim 2003, Schoepp 2004).

DNA probes, microarray platform: Assays using immobilized oligonucleotides in a microarray have been developed to identify and discriminate among orthopoxviruses (see References: Lapa 2002, Laassri 2003).
Serology: Antibodies appear 6 to 8 days after infection. Classical methods such as complement fixation and gel precipitation commonly were used in the past. Experimental enzyme-linked immunoassays have been developed more recently (see References: LeDuc 2001).

Rapid Tests for Diagnosis of VZV and HSV

Laboratories that have at least BSL-2 containment facilities can perform rapid tests for diagnosis of rash illness in patients not considered at high risk for smallpox. Local or state LRN laboratories should be contacted for testing of specimens from patients with a moderate or high risk of smallpox (see Criteria for Determining the Likelihood of Smallpox above). The most likely alternative agents are varicella-zoster virus (VZV) and herpes simplex virus (HSV); available rapid tests for these two agents include the following:

Cytology smears: Tzanck preparations stained with Giemsa or Papanicolaou stain can be used to differentiate VZV or HSV, each of which forms multinucleated giant cells, from smallpox, which does not. The testing is rapid, inexpensive, and relatively sensitive (see References: Cohen 1994, Gershon 1999, Koranda 2005, Oranje 1986).
Direct fluorescent antibody (DFA): An assay by Chemicon (see References: Chemicon, Inc) detects VZV and HSV simultaneously. A recent study shows a sensitivity of 80% and specificity of 98.3% for HSV with same-day turnaround. A shell vial direct immunoperoxidase assay had a sensitivity of 87.6% and a specificity of 100%, and a turnaround time of 1 to 2 days. With VZV-positive samples, the DFA had a correlation of 87.1% with a cytospin DFA method (see References: Chan 2001). DFA was instrumental in ruling out 3 of 4 cases with moderate risk for smallpox in the United States during 2002 (see References: CDC: Smallpox and vaccinia laboratory testing: a national training initiative).
Electron microscopy: Although electron microscopes and operators experienced in viral recognition are not widely available, EM can play a role in the rapid diagnosis of rash illness (see References: Madeley 2003).
Standard PCR methods: PCR has been shown to be more sensitive than immunofluorescence for detection of VZV (see References: Bezold 2001) and significantly more sensitive than electron microscopy (see References: Jain 2001). PCR has been shown to detect HSV and VZV effectively from Tzanck smears and vesicle fluid but less effectively from fixed-tissue specimens (see References: Nahass 1995). FDA-approved methods are not yet available.
Real-time PCR assays: Rapid PCR assays using TaqMan and LightCycler technologies have been developed for HSV and VZV. These assays appear to have very high sensitivity and specificity (see References: Espy 2000, Hawrami 1999, Ryncarz 1999, Aldea 2002, Koenig 2001, Nicoll 2001).

Testing in Areas With Confirmed Smallpox

Once smallpox is confirmed in a geographic area, additional cases can be diagnosed clinically (see References: CDC: Smallpox response plan and guidelines: Guide A).

In such situations, laboratory resources will be used for specimen testing in the following cases:

Those in which clinical presentation is unclear
Those that will provide information about a potential source of exposure
Those that will facilitate law enforcement activities or case detection

Inadvertent Discovery of Variola Virus in a Laboratory Specimen

Variola virus and other poxviruses grow readily on many cell lines such as Vero, HeLa, SF, and MRC-5. Accidental discovery of variola virus by a clinical virologist would constitute a danger to the laboratorians and could precipitate unintentional release to the community. The following features of variola virus in cell culture have been described in the older literature (see References: Fenner 1988: Chapter 2; Marennikova 1974; Ono 1968):

In human cell lines, variola virus tends to form "hyperplastic foci" as cells are pushed together by growing cells around them.
Within 24 to 48 hours, giant multinucleated cells form.
When stained, there may be a circular arrangement of nuclei around an eosinophilic part of the cytoplasm, often containing inclusions.
Within 72 to 96 hours, the number of giant cells increases, as does degeneration of the cell layer.
Variola virus can cause numerous inclusion bodies (Guarnieri bodies) in the cytoplasm of infected cells, which can be viewed after staining by Giemsa, modified silver stain, or other stains. Interpretation was difficult during times of smallpox occurrence and would be more difficult today.
If an unusual cytopathic effect is observed on any cell culture, especially involving giant cells, laboratory personnel should determine the suspected diagnosis for the patient before proceeding with identification. If the patient is at high risk for smallpox or at moderate risk for smallpox without alternate diagnoses, then the cell culture should be sealed, stored securely, and the local or state health department contacted for further instructions. Staining of cells suspected of harboring poxvirus is not recommended.

Treatment

Treatment for smallpox largely consisted of general supportive measures:

Adequate fluid intake (difficult because of the enanthem)
Alleviation of pain and fever
Keeping the skin lesions clean to prevent bacterial superinfection

No specific antiviral treatment of demonstrated effectiveness was available in the pre-eradication era.

In recent years, other compounds have been evaluated; cidofovir, adefovir dipivoxil, cyclic cidofovir, and ribavirin have shown significant in vitro activity against variola virus (see References: Franz 1997). Recent studies, however, suggest that patients may require a higher dose of cidofovir than is currently licensed for humans and may also require probenicid to ameliorate the uptake of cidofovir by renal tubular epithelial cells (see References: McSharry 2008).

Another agent, ST-246 (formerly SIGA-246), is a low-molecular-weight compound that is active against multiple orthopoxviruses, including variola virus (see References: Grosenbach 2008; Jordan 2008; NIAID 2006: A double-blind, randomized, placebo-controlled, ascending single-dose, phase 1 trial; Quenelle 2007; SIGA Technologies 2006; SIGA Technologies 2008, Yang 2005). The drug was used (along with vaccinia immune globulin and cidofovir) in a recent case of eczema vaccinatum in a 2-year-old boy (see References: SIGA Technologies 2007; Vora 2008). The child recovered fully after a 48-day hospitalization.
Chimpanzee-human monoclonal antibodies (mAb) may be useful in preventing and treating vaccinia virus–induced complications of vaccination against smallpox and as immunoprophylaxis and immunotherapy for smallpox (see References: Chen 2006, Chen 2007).

Smallpox Vaccination

Historical Perspective

The first efforts at smallpox vaccination involved a process called variolation, which was the deliberate cutaneous inoculation of variola virus via infectious material obtained from smallpox pustules of a patient with active disease (see References: Fenner 1988: Chapter 6). Variolation was practiced as early as 1000 AD in China and gradually spread around the globe.
In the late 1700s, Edward Jenner successfully used cowpox virus to vaccinate people against smallpox. Because this practice was safer and relatively effective, it rapidly gained wide acceptance and replaced variolation as the primary method of conferring protection against smallpox.
Over time, vaccinia virus gradually replaced cowpox virus as the agent used in smallpox vaccine. Vaccinia virus is genetically distinct from cowpox virus, although its origin remains unknown. It may have been derived from cowpox virus initially and modified over time through serial passage in laboratory cultures, or it may represent another orthopoxvirus that is now extinct in nature.
Until February 2008, the vaccinia vaccine available in the United States was a lyophilized preparation of infectious vaccinia virus (Dryvax, manufactured by Wyeth Pharmaceuticals, Inc., Marietta, Pennsylvania). All lots of Dryvax vaccine expired on February 29, 2008, and programs that held supplies of Dryvax vaccine were instructed to destroy those supplies by March 31, 2008 (see References: CDC: Newly licensed smallpox vaccine to replace old smallpox vaccine).

The duration of vaccine immunity for Dryvax has never been adequately measured. Epidemiologic studies suggest that protection against smallpox persists for at least 5 to 10 years after primary vaccination (and perhaps longer).
Additional studies suggest that individuals vaccinated in the past with the Dryvax vaccine appear to maintain clinically detectable immunity against vaccinia for at least 20 years (see References: Simpson 2007, Viner 2005).
It is not clear whether a remote history of receiving at least one dose of smallpox vaccine will modulate disease severity in the event that infection occurs.
It has been estimated that less than 20% of persons vaccinated before the early 1970s (when routine vaccination was discontinued in the United States) have immunologic protection today (see References: Henderson 1999: Smallpox as a biological weapon).
Intradermal skin testing with inactivated vaccinia virus may be a simple and reliable method for predicting residual immunity to smallpox (see References: Kim 2006).

ACAM2000

ACAM2000 (Acambis, Inc, Cambridge, Massachusetts), is a live vaccinia virus smallpox vaccine that was licensed for use in the United States by the Food and Drug Administration in August 2007 (see References: Acambis 2007; FDA 2007: FDA approves new smallpox vaccine; Acambis 2008). ACAM2000 has replaced Dryvax smallpox vaccine because of withdrawal of the Dryvax license. The vaccine is derived from plaque purification cloning from Dryvax.

A recently completed Phase 2 clinical trial demonstrated that at a dose of 6.8 x 10⁷ pfu/mL, ACAM2000 elicited a successful immune response in 94% of subjects, which was similar to the proportion of subjects (96%) who responded to Dryvax vaccine (at a dose of 1.6 x 10⁸ pfu/mL) (see References: Artenstein 2005).

CDC will continue to provide ACAM2000 smallpox vaccine to protect responders as part of state public health preparedness programs and civilian laboratory personnel who risk exposure to orthopoxviruses. Unlike Dryvax, ACAM2000 expires 18 months after release from the CDC Strategic National Stockpile. Acambis has supplied 195.2 million does of ACAM2000 to the US government for its Strategic National Stockpile (see References: Acambis 2008). Currently, there is enough vaccine in the stockpile for all Americans (see References: HHS: Project Bioshield: Medical countermeasures for smallpox).

New Vaccines

One approach is to develop vaccines derived from attenuated vaccinia-derived viruses (see References: Belyakov 2003, Poland 2003).The highly attenuated modified vaccinia Ankara (MVA) is a possible alternative that is safer than Dryvax but may not be as immunogenic (see References: Earl 2004, Earl 2008, McCurdy 2004, Parrino 2007, Slifka 2005, Vollmar 2006).

In phase 1 and 2 clinical trials, IMVAMUNE (an MVA vaccine) was highly immunogenic and safe with no unexpected side effects or serious adverse effects reported in either healthy volunteers, immunocompromised (HIV) patients, or volunteers with atopic dermatitis. Additional phase 2 trials are ongoing in these groups, and more phase 2 trials are planned for 2009 (see References: Jones 2008).
The US government announced in June 2007 that it would acquire 20 million doses of MVA from Bavarian Nordic of Copenhagen, Denmark, for the Strategic National Stockpile for use in healthy and immunocompromised people (see References: HHS buys next generation smallpox vaccine).

In Japan, a highly attenuated smallpox virus (LC16m8) was used in infants in the early 1970s. Unfortunately, the strain was found to spontaneously revert to a more virulent parent strain.

Investigators recently identified the gene responsible for virulence reversion (B5R) and deleted it. In a mouse model, vaccine produced from the deletion strain provided similar immunogenicity to Dryvax vaccine and was much more immunogenic than MVA vaccine (see References: Kidokoro 2005).
A phase 2 trial, involving 153 naive volunteers, comparing the safety and immune response of LC16m8 to that of Dryvax has been completed and showed that 100% of those receiving LC16m8 and 86% of those receiving Dryvax experienced a "take" and seroconversion (see References: Wiser 2007).

A number of other studies on possible candidate vaccines (such as cell culture vaccines, subunit vaccines, and recombinant vaccines) have been published in the last several years, and research into new vaccines is ongoing.

Recommendations for Use of Vaccinia Vaccines

The current CDC strategy for use of the vaccine in outbreak control is outlined under Use of Smallpox Vaccine During a Smallpox Emergency below.
Routine smallpox vaccination in the United States stopped in 1972 for children and in 1976 for healthcare workers. Prior to 1972, smallpox vaccine was recommended for all children in the United States at 1 year of age. The US military continued to vaccinate new trainees against smallpox until 1990 when vaccination was discontinued.
Since that time, vaccinia vaccination has been recommended for laboratory workers and certain healthcare workers:

Vaccination is recommended for those who directly handle vaccinia virus cultures, contaminated dressings or other infectious material, recombinant vaccinia viruses, or other orthopoxviruses that infect humans (eg, monkeypox). A recent report described an unvaccinated laboratory worker in whom ocular vaccinia developed while he was working with multiple strains of vaccinia virus (see References: 2004: Ocular vaccinia infection in laboratory worker). The worker was an immunology graduate student who was conducting research as part of a thesis project. This case highlights the importance of biosafety practices and vaccination among those who work with these viruses in the laboratory setting.
Vaccine also is recommended for those who handle animals contaminated or infected with vaccinia virus, recombinant vaccinia viruses, or other orthopoxviruses that infect humans.
Five cases of laboratory-acquired vaccinia exposures and infections were reported to the CDC between 2005 and 2007, underscoring the need for proper vaccination, laboratory safety, infection-control practices, and rapid medical evaluation of exposures among laboratory personnel (see References: CDC: Laboratory-acquired vaccinia exposures and infections).

In December 2002, the US smallpox vaccination policy was changed to include the following:

Required smallpox vaccinations for military personnel.
Smallpox vaccination for "smallpox response teams" involving civilian public health staff and healthcare workers likely to be involved in the initial care of any patients with smallpox. (See further information about smallpox response teams in the next section.)

The US Smallpox Vaccination Program

To enhance preparedness in the event of a smallpox emergency, in October 2002 the Advisory Committee on Immunization Practices (ACIP) and the Healthcare Infection Control Practices Advisory Committee (HICPAC) recommended smallpox vaccination for persons designated by the appropriate bioterrorism and public health authorities to conduct investigation and follow-up of initial smallpox cases (ie, smallpox response teams). These teams were to include medical team leaders, public health advisors, medical epidemiologists, disease investigators, diagnostic laboratory scientists, nurses, personnel who would administer smallpox vaccines, and security/law enforcement personnel (see References: CDC: Recommendations for use of smallpox vaccine in a pre-event smallpox vaccination program).

According to CDC, 39,608 persons were vaccinated through the program as of October 31, 2005, which is the last date that information is available on the CDC Web site (see References: CDC: Smallpox vaccination program status by state). Less than 17% of smallpox vaccine doses distributed to states for healthcare workers had been used by mid-2005 (see References: Bass 2007).

Reasons for non-participation in the program included the relatively low risk of a smallpox outbreak, risks associated with vaccination, hospital costs, and high rates of contraindications to vaccination (see References: Kemper 2005, Wortley 2006).
Public health departments achieved significantly higher vaccination rates than did hospitals (see References: Lindley 2006).

Vaccination Schedule

Vaccination consists of a single dose followed by a booster every 10 years.
Revaccination every 3 years (see References: CDC: Vaccinia [smallpox] vaccine) should be considered for persons who work with:

Nonhighly attenuated vaccinia viruses
Recombinant viruses developed from nonhighly attenuated vaccinia viruses
Nonvariola orthopoxviruses such as monkeypox

Dosage and Route of Administration

Before smallpox vaccine is administered, patients should be screened for contraindications and provided with educational information about the vaccine (see References: CDC: Smallpox pre-vaccination information packet).

The vaccine is administered using a droplet of the vaccine applied to a bifurcated needle. This procedure is detailed by CDC (see References: CDC: Smallpox vaccination method; CDC: Smallpox vaccine administration video).

Choose the site for vaccination; the deltoid area on the upper arm is preferred (although a recent study found that the upper inner arm also may be a suitable site and may be the preferred site in some instances [see References: Waibel 2006]).
No skin preparation is required. Under no circumstances should alcohol be applied to the skin prior to vaccination, as it has been shown to inactivate the vaccine virus.
Dip the needle into the vaccine vial and withdraw. The same needle should never be dipped into the vaccine vial more than once, in order to avoid contamination of the vial.
Hold the needle perpendicular to the site of insertion.
For primary vaccinations, make three insertions (perpendicular strokes) of the needle rapidly in an area about 5 mm in diameter; for revaccinations, make 15 insertions of the needle (see References: CDC: Recommendations for use of smallpox vaccine in a pre-event smallpox vaccination program). The strokes should be sufficiently vigorous so that a trace of blood appears at the vaccination site after 15 to 30 seconds. If no blood is visible, an additional three insertions should be made using the same bifurcated needle without reinserting the needle into the vaccine vial.
Discard the bifurcated needle in an appropriate biohazard container immediately after vaccinating a patient.
Absorb the excess vaccine and blood from the site with sterile gauze and discard in a safe manner (usually in an infection control receptacle).
Cover the site with a sterile gauze dressing (or similar absorbent material) loosely secured by tape. This dressing should be covered with a semipermeable dressing. Products that combine an absorbent base with an overlying semipermeable layer also can be used to cover the vaccination site.
Educate the vaccinee about caring for the site (see section Smallpox Vaccination Clinic Implementation below and see References: CDC: Caring for the smallpox vaccination site).
Record the following information: vaccine used, diluent used, lot number, and any adverse health events.

Local Reaction to Vaccination

Upon primary vaccination, all recipients experience a local reaction to the vaccine. A typical reaction occurs in the following sequence (see References: CDC: Smallpox vaccination and adverse events training module; CDC: Smallpox vaccination and adverse reactions: guidance for clinicians):

At 3 to 5 days after vaccination, a red papule appears at the vaccination site.
By day 5 to 8, the papule becomes vesicular, then pustular, and reaches its maximum size at 8 to 10 days. The jennerian pustule, which contains turbid fluid, is whitish, umbilicated, multilocular, and surrounded by an erythematous areola.
The pustule eventually dries, leaving a dark crust that normally separates 14 to 21 days after vaccination.
A pitted scar usually remains after the scab separates.
Regional lymphadenopathy and fever are common.
Response to the vaccination should be evaluated 6 to 8 days after vaccination to assure that a typical reaction has occurred (ie, a "take").
A mouse model has demonstrated that vaccination initially (up to 4 days) induces infiltration of macrophages at the site, followed by granulocytes and lymphocytes. After that time, a large recruitment of CD4+ and CD8+ T cells occurs (see References: Jacobs 2006).

Cutaneous reactions to subsequent vaccinations are weaker and manifest a range of the local reactions above. For a revaccination to be considered successful, palpable inflammation or a pustule must be present. With revaccination, the less intense the jennerian pustule, the greater the likelihood of some degree of residual immunity. Vaccinated persons in whom a typical reaction to the vaccine develops are considered to be protected against smallpox, since more than 95% of such persons have been shown to have increased antibody titers following vaccination. No reaction to revaccination indicates inadequate technique or insufficient virus in the inoculation.

Contraindications and Precautions

Vaccinia vaccine for preexposure use is contraindicated for the following groups (see References: CDC: Recommendations for use of smallpox vaccine in a pre-event smallpox vaccination program):

Persons who have ever been diagnosed with eczema or atopic dermatitis (even if the condition is mild or not presently active), because the risk of eczema vaccinatum is increased.

The increased risk may be related to immunologic abnormalities such as altered adaptive immunity or defects in innate immune responses (see References: Engler 2002).
Experiments in a mouse model suggest that susceptibility to eczema vaccinatum after contact with vaccinia virus in the presence of atopic dermatitis is related to ineffective antiviral immune responses (see References: Freyschmidt 2007). The allergic inflammation associated with atopic dermatitis appears to be associated with dysregulated immunity to vaccinia virus.

Persons with other acute or chronic exfoliative skin conditions (eg, burns, impetigo, chicken pox, contact dermatitis, shingles, herpes, severe acne, psoriasis), until the condition resolves
Persons with conditions causing immunodeficiency (eg, HIV infection, leukemia, lymphoma, generalized malignancy, solid organ or stem cell transplant, agammaglobulinemia or other hereditary immunodeficiency, autoimmune disease); for more information on smallpox vaccination and patients with organ transplantation, see References: Dropulic 2003. A new vaccine has been developed for use in immunocompromised individuals (see References: Bavarian Nordic 2007: IMVAMUNE; Dorrell 2007).
Persons receiving treatments that cause immunodeficiency (eg, alkylating agents, antimetabolites, radiation, corticosteroids, chemotherapy agents, organ transplant medications); persons who are taking or have taken high-dose corticosteroids should not be vaccinated within 1 month of completing therapy, and persons treated with other immunosuppressive drugs within the last 3 months should not be vaccinated
Pregnant women, because vaccination may result in stillbirth or death of the infant shortly after delivery

Before vaccination, women of childbearing age should be asked if they are pregnant or intend to become pregnant in the next 4 weeks—those who respond positively should not be vaccinated (for more information on smallpox vaccine and pregnancy, see References: CDC: Smallpox vaccination information for women who are pregnant or breastfeeding; CDC 2003: Smallpox vaccination and adverse reactions; Nishiura 2006: Smallpox during pregnancy).
In a smallpox bioterrorism emergency, pregnant women at high risk of exposure should be advised to be vaccinated, since the risk of death and serious illness from smallpox in that situation would likely outweigh risks to fetus from fetal vaccinia (see References: Cono 2006).
A study of 376 women enrolled in the National Smallpox Vaccine in Pregnancy Registry showed that women vaccinated during pregnancy did not have higher-than-expected rates of pregnancy loss, preterm birth, or birth defects compared with those in healthy referent populations. Most of the women in the registry (77%) were vaccinated near the time of conception, before results of a standard pregnancy test would have been positive. No cases of fetal vaccinia have been identified (see References: Ryan 2008: Pregnancy, birth, and infant health outcomes).
A retrospective cohort study employing information from Department of Defense databases examined outcomes among 31,420 infants born to active-duty military women during 2003-04 (see References: Ryan 2008: Evaluation of preterm births and birth defects). Analysis revealed that maternal smallpox vaccination during pregnancy was not associated with preterm or extreme preterm delivery. Maternal smallpox vaccination in the first trimester was not significantly associated with overall birth defects or of seven specific birth defects individually modeled.

According to the product labeling, smallpox vaccination is not recommended for women who are breast-feeding
Persons with hypersensitivity reactions to vaccine components, including polymyxin B sulfate, streptomycin sulfate, chlortetracycline hydrochloride, and neomycin sulfate
Persons under 18 years of age in nonemergency situations
Persons with household contacts who are immunodeficient, who have a history of eczema or atopic dermatitis (even if the condition is not currently active), or who have an acute, chronic, or exfoliative skin condition
Persons with physician-diagnosed cardiac disease, with or without symptoms or with three or more major risk factors for cardiac disease (hypertension, diabetes, hypercholesterolemia, heart disease at age 50 years in a first-degree relative, smoking) (see References: CDC: Supplemental recommendations on adverse events following smallpox vaccine in the pre-event vaccination program)

Vaccine Distribution and Storage

Smallpox vaccine is available from CDC through state or local health departments to appropriate clinic sites. Key points for consideration include the following (see References: CDC: Information to support public health and clinical personnel planning for smallpox vaccination):

Each vaccine kit contains the necessary supplies to vaccinate 100 persons, including a vial of vaccine, diluent, and 100 bifurcated needles.
The vaccine vial holds 100 doses of vaccine after reconstitution; the vial is about 1.5 in. tall and about 5/8 in. in diameter.
If additional bifurcated needles are needed, they may be obtained through the Strategic National Stockpile at the number provided in the shipping instructions.
Both unreconstituted and reconstituted vaccine should be stored at between 2°C and 8°C when not in use. It may be kept at normal room temperature during the course of a clinic session and then placed back into refrigeration. A recent study indicated that vaccine titers remain higher if the vaccine is kept on ice when not in refrigeration (see References: Kline 2005).
The vaccine is good for 90 days after being reconstituted and may be taken in and out of refrigeration as many times as needed during the course of those 90 days.
The vaccine is not light-sensitive, so no special measures are needed to protect against light exposure.

Vaccination of Healthcare Workers

Management of the vaccination site

Vaccinated healthcare workers who are involved in direct patient care should keep the vaccination site covered with gauze or similar absorbent material, because vaccinia has been detected through at least day 21 after vaccination (see References: Cummings 2008). This dressing should then, in turn, be covered with a semipermeable dressing that provides a barrier for containment of vaccinia virus to minimize the risk of transmission. Alternatively, products combining an absorbent base with an overlying semipermeable layer can be used to cover the site. The latter may be preferable, because it has been found to more effectively reduce viral passage to the external surface of the dressing (see References: Savona 2007).The vaccination site should be covered with gauze, a semipermeable dressing, and a layer of clothing during direct patient care until the scab separates.
Vaccinated healthcare workers should be reminded that consistent hand hygiene with antimicrobial soap and water or an approved alcohol-based hand rub is critical for preventing contact transmission.

When to recommend administrative leave for vaccinated healthcare workers

Vaccinated healthcare workers do not need to be placed on administrative leave unless they: (1) are physically unable to work because of systemic signs and symptoms of illness, (2) have extensive skin lesions that cannot be adequately covered, or (3) are unable to adhere to the recommended infection control precautions.

Administration of other vaccines and PPD testing

Smallpox vaccine may be administered at the same time as any inactivated vaccine and at the same time as other live-virus vaccines except varicella vaccine (varicella vaccine and vaccinia vaccine should be given at least 4 weeks apart). Parenterally administered live vaccines not given on the same day as smallpox vaccine should be given 4 or more weeks later.
Healthcare workers who are due to receive an annual PPD skin test should not receive the test until 1 month after smallpox vaccination.

Use of Vaccine for Postexposure Prophylaxis

Immunity to variola virus generally develops within 8 to 11 days after vaccination. Since the incubation period for smallpox averages about 12 days, vaccination soon after exposure (ie, within 4 days) may confer some immunity to exposed persons and reduce the likelihood of a fatal outcome.
Postexposure vaccination may be particularly useful for persons who have received a dose of vaccine at some point in the past, since such persons are more likely to mount an anamnestic immune response with revaccination (see References: Henderson: Smallpox as a biological weapon).
Studies on the utility of postexposure vaccination have shown conflicting results. Examples of study findings include the following:

In one study in Italy in 1946, 21 contacts who received vaccine within 5 days after exposure and in whom smallpox subsequently developed all had mild disease, whereas 31 contacts who were vaccinated 6 to 10 days after exposure had a case-fatality rate of 19% (see References: Dixon 1948). These findings suggest a protective effect for postexposure vaccination only if vaccine is administered within several days after exposure.
In another study involving 34 patients vaccinated during the incubation period, nine were vaccinated at least 8 days before illness onset; four (44%) of these patients died. Twenty-five were vaccinated 7 or fewer days before illness onset; 10 (40%) of these patients died (see References: Guha Mazumder 1975).

How late after exposure individuals can be vaccinated and not become ill is unclear.

Use of Vaccine During a Smallpox Emergency

During the smallpox eradication campaign and during smallpox outbreaks in the past, a "ring vaccination" strategy has been followed. This approach is incorporated into the current CDC Smallpox Plan (see References: CDC: Smallpox response plan and guidelines: Guide B). Ring vaccination essentially involves creating a circle of vaccinated persons around each case to interrupt the chain of transmission. The strategy involves the following steps:

Rapid identification and isolation of all smallpox cases
Identification and vaccination of contacts of smallpox cases
Monitoring contacts for development of fever and isolating them if fever occurs
Vaccination of household members of contacts if no contraindications to vaccination exist

In addition to ring vaccination, rapid voluntary vaccination of a large population may be required to:

Supplement priority surveillance and containment control strategies in areas with smallpox cases
Reduce the "at-risk" population for additional intentional releases of smallpox virus if the probability of such occurrences is considered significant.
Address heightened public or political concerns regarding access to voluntary vaccination

Large-scale voluntary smallpox vaccination would only be initiated in certain situations under recommendations from the Secretary of HHS. Wide-scale quarantine of communities likely would not be effective and, therefore, would not be recommended (see References: Barbera 2001).

Guide B of the CDC smallpox guidelines provides detailed information on use of smallpox vaccine during an emergency situation (see References). Key points for vaccine use are outlined in the table below.

Vaccination Guidelines for Use of Smallpox Vaccine During a Smallpox Emergency^a

Whom to vaccinate:
—Persons exposed to the initial release of the virus
—Persons who had face-to-face, household, or close proximity contact (ie, up to 6.5 ft) with a confirmed or suspected smallpox patient after fever develops in patient and until all scabs have separated (no longer infectious)
—Healthcare personnel, public health personnel, first responders, law enforcement personnel, and others whose jobs put them at increased risk of exposure to smallpox.
—Laboratory personnel selected for collection or processing of clinical specimens from confirmed or suspected smallpox cases
—Other persons with increased likelihood of contact with infectious materials from a smallpox patient, such as laundry or medical-waste handlers for a facility where smallpox patients are admitted
—Other groups whose unhindered function is deemed essential to maintaining basic community needs (eg, transportation, pharmacy) or response activities and who are not otherwise involved in patient-care activities but who have a reasonable probability of contact with smallpox patients or infectious materials (eg, law enforcement, emergency response, military personnel)
—Because of potential for greater spread of smallpox in a hospital setting due to possible aerosolization of virus from a severely ill patient, vaccination should be considered for those individuals present in the hospital during the time that a case was present and not yet isolated in an appropriate manner in a room with ventilation separate from other areas of the hospital

Persons with contraindications for vaccination but not in a situation likely to encounter a smallpox case^a,b:
—Persons who have ever been diagnosed with eczema or atopic dermatitis, even if the condition is mild or not presently active
—Persons with other acute or chronic exfoliative skin conditions such as burns, impetigo, or varicella-zoster (shingles), herpes, severe acne, severe diaper dermatitis with extensive areas of denuded skin, or psoriasis should not be vaccinated until the condition resolves
—Persons with diseases or conditions that cause immunodeficiency
—Persons with inflammatory eye disease being treated with steroids
—Women who are pregnant or breast-feeding
—Persons with serious, life-threatening allergies to the antibiotics polymyxin B, streptomycin, tetracycline, or neomycin

^aGenerally, those with vaccine contraindications who have face-to-face contact with a smallpox patient are at greater risk for development of smallpox than for complications from vaccination and should be considered for vaccination.
^bPersons who have contraindications to vaccination and who are household members of contacts who receive vaccine should consider housing themselves separately from vaccinated household members, to avoid potential exposure to smallpox or inadvertent inoculation with vaccine virus, until their vaccination sites have healed. This will decrease risk of contact transmission through vaccination site.

Adapted from CDC: Smallpox response plan and guidelines: Guide B (see References).

Guidelines for large-scale smallpox vaccination clinics can be found in Annex 3 of the Smallpox Response Plan and Guidelines (see References). This guide includes the following information:

Vaccine delivery and packaging logistics
Organization of a large-scale vaccination clinic
Logistics for IND administration of smallpox vaccine
Question and answer sheets on smallpox vaccine for the general public
Considerations for mass patient care

Smallpox Vaccination Clinic Implementation

In general, smallpox vaccine clinics should follow standard operating procedures for administration of other vaccines. CDC has provided information about operating postexposure vaccination clinics (See References: CDC: Smallpox response plan: Annex 3: Smallpox vaccination clinic guide; CDC: Community-based mass prophylaxis: a planning guide for public health preparedness). In addition, CDC has provided software programs (Maxi-Vac 1.0 and Maxi-Vac Alternative) that can be used by state and local public health officials to plan large-scale smallpox vaccination clinics with maximum patient flow-through. The programs can be downloaded for free from the CDC Web site (see References: CDC: Download Maxi-Vac version 1.0 and Maxi-Vac alternative).

Special considerations for smallpox clinics (including hospital-based clinics in the pre-event setting include the following:

Vaccinators:

May include those allowed to administer vaccines under state law.
Should receive smallpox vaccine themselves.
Should receive standardized training in administration of smallpox vaccine, including use of bifurcated needles.

Supplies:

Vaccine, diluent, and bifurcated needles are available from CDC.
Once a person has received the vaccine, the vaccination site must be covered loosely with a gauze bandage. Each clinic must provide its own bandages; these are not available from CDC.

Vaccine recipients:

Potential vaccine recipients should be pre-screened for contraindications, provided information about the vaccine, and educated about care of the vaccination site to avoid auto-inoculation of vaccinia virus to another body site or contact transmission to others (see References: CDC: Caring for the smallpox vaccination site; CDC: Smallpox pre-vaccination information packet). Key points regarding care of the vaccination site include:

Avoid rubbing or scratching the vaccination site and don't apply ointments or salves to the site.
Keep the site loosely covered with a gauze bandage; do not use a bandage that blocks all air from the vaccination site.
Change the dressing every 1 to 2 days.
Wash hands with soap and water after contact with the vaccination site or contaminated bandages.
Keep the vaccination site dry.
Put contaminated bandages in a sealed plastic bag and throw them away.
Wash clothing or other material that comes in contact with the vaccination site.

Vaccinees should return to the clinic 7 days after vaccination so the site can be assessed to determine whether or not the vaccination has been successful. One recent report found that self-evaluation may be feasible to assess the presence an appropriate skin reaction that demonstrates a "take" of the vaccine (see References: Huerta 2006).
Vaccinees also should be given information about severe side effects and when medical care should be sought.
CDC developed and used until recently the Hospital Smallpox Vaccination Monitoring System (HSVMS) for tracking adverse reactions to smallpox vaccination among hospital employees. Data from the HSVMS collected between February and August 2003 showed that adherence to recommended vaccination site care was high (88.4%) and that the number of days of work lost related to vaccination was low (see References: Klevens 2005).
An electronic monitoring system for self-reporting of adverse events among military vaccinees was evaluated in a prospective cohort of vaccinated subjects (see References: Olmsted 2005). The sensitivity and positive predictive value of self-reports were shown to be 98.9% and 99.6%, respectively. These findings suggest that electronic self-reporting could be useful during a mass vaccination event.

Adverse Events Following Smallpox Vaccination

Historic Perspective

Serious adverse reactions to smallpox vaccination can occur (see References: CDC: Adverse reactions following smallpox vaccination; Lane 2003). For images of smallpox vaccine reactions, see References: CDC: Smallpox: vaccine and adverse events training module.

Well-documented adverse reactions from historical information (ie, before routine vaccination ceased in the United States) include the following:

Tenderness, erythema at the injection site and other localized reactions (including allergic reactions to tape adhesives), and secondary bacterial infections; local reactions greater than 10 cm in size are referred to as "robust takes"
Systemic reactions: Fever of at least 100°F, malaise, myalgias, local lymphadenopathy
Various dermatologic reactions, including erythema multiforme and Stevens Johnson syndrome
Inadvertent autoinoculation of another body site: 25.4 to 529.2 cases per million primary vaccinees
Generalized vaccinia (GV): Vesicles or pustules appearing on normal skin distant from the vaccination site; 23.4 to 241.5 cases per million primary vaccinees
Eczema vaccinatum (EV): Localized or systemic spread of vaccinia virus; may be severe and can be fatal; 10.4 to 38.5 cases per million primary vaccinees
Vaccinia keratitis
Progressive vaccinia (PV): Progressive necrosis in the area of vaccination, often with metastatic lesions at other sites; can be severe and fatal; 0.9 to 1.5 cases per million primary vaccinees) (see References: Bray 2003)
Postvaccinial encephalitis (PVEM): 2.9 to 12.3 cases per million primary vaccinees
Fetal vaccinia: Occurs after primary inoculation of the mother during pregnancy; usually results in stillbirth or death of the infant soon after birth
Death: An estimated 1.1 deaths per million primary vaccinees, but this may depend on strains used for vaccines. An analysis of recent smallpox vaccination studies from the 1950s to the present in different countries has suggested that strain-related differences exist in death rates (eg, 8.4 deaths per million vaccinees for the Lister strain [see References: Kretzschmar 2006]). The Bern strain (used in Germany and Austria in the 1950s) gave the highest estimate of deaths per million vaccinations (55) and the New York City Board of Health Strain the lowest (1.4).
Note: Myopericarditis was not noted as an adverse event in the past but has been documented more recently, as outlined in the section below on recent experience.

Adverse event rates tend to be much lower in revaccinees compared with primary vaccines (see References: Treanor 2006).

Recent Experience

Myopericarditis and Cardiac Adverse Events

In addition to previously recognized adverse events, more recent experience with smallpox vaccine has demonstrated that myopericarditis is a potential adverse event. The etiology of postvaccination myopericarditis remains unclear, although it appears that the process is immunologically mediated rather than the result of direct viral infection of the myocardium. Epidemiologic studies have supported a causal relationship between myocarditis/pericarditis and smallpox vaccination (see References: Neff 2008).

Among more than 1,200,000 military personnel vaccinated between December 13, 2002, and May 17, 2007, 140 cases of myopericarditis were identified, yielding a rate of approximately 117 cases per million vaccinees (see References: Eckart 2004; DoD 2007); follow-up of 64 cases (63%) demonstrated that all patients had normalization of cardiac function at an interval of 32 +/- 16 weeks.
In addition to myopericarditis, 16 cases of ischemic cardiac events have been reported following smallpox vaccine administration to military personnel. Poland and colleagues (see References: Poland 2005) conclude: "The available data do not support a causal association between ischemic cardiac events and receipt of smallpox vaccine; however, this possibility cannot be excluded."
Follow-up studies of 37,901 HHS smallpox vaccinees revealed myocarditis or pericarditis in 21 vaccinees; 18 cases occurred among those who had been revaccinated. Myocarditis was mild with no fatalities, although nine patients were hospitalized (see References: Morgan 2008). Ischemic cardiac events occurred in 10 patients (six myocardial infarctions [two resulted in sudden death] and four cases of angina) (see References: Swerdlow 2008). The observed number of myocardial infarctions exceeded estimated expectations but remained within the 95% predictive interval.

Neurologic Adverse Events

Neurologic adverse events associated with smallpox vaccination as identified through active case reporting and VAERS between December 2002 and March 2004 demonstrated the following (for both civilian and military vaccinees) (see References: Sejvar 2005):

Headache (95 cases), followed by nonserious limb paresthesias (17 cases) or pain (13 cases) and dizziness or vertigo (13 cases)
Serious adverse events

Suspected meningitis (13 cases)
Encephalitis or myelitis (3 cases)
Bell palsy (11 cases)
Seizures (8 cases, including 1 death)
Guillain Barre syndrome (3 cases)

The authors stated that no neurologic syndrome was identified at a rate above estimated baseline and serious adverse events occurred in accordance with expected ranges.

Dermatologic Adverse Events

Several anecdotal reports have recently been published regarding dermatologic adverse events following smallpox vaccination.

New dermatologic conditions identified following vaccination include urticaria, exanthems, contact dermatitis, and erythematous papules (see References: Greenberg 2004) as well as focal and generalized suppurative folliculitis (without evidence of viral infection and mistakable for generalized vaccinia) (see References: Talbot 2003).
One recent study involving 11,058 vaccinees at Fort Hood, Texas, found that six had hypersensitivity reactions, including an exanthematous reaction pattern (three vaccinees), an urticarial reaction pattern (two vaccinees), and an erythema multiforme–like pattern (one vaccinee) (see References: Bessinger 2007).
A range of benign dermal abnormalities have been reported at the vaccination site, including exaggerated scarring (hypertrophic or keloidal), dermatofibroma, and nevus sebaceous (see References: Waibel 2006: Smallpox vaccination site complications; Waibel 2006: Smallpox vaccination site reactions).
Malignant tumors at the smallpox vaccination site also have been reported, including basal cell carcinoma, malignant melanoma, squamous cell carcinoma, and fibrohistiocytic tumors (see References: Waibel 2006: Smallpox vaccination site complications). Such lesions may occur as the result of scarring followed by malignant degeneration, although a causal relationship between vaccination and dematological malignancies has not been established.

Other events

A report involving US military personnel identified possible generalized vaccinia in 50 cases (66 cases per million vaccinees), although none met a strict case definition for confirmed or probable generalized vaccinia (see References: Lewis 2006: Analysis of cases reported as generalized vaccinia during US military smallpox vaccination program).

Severe adverse events following smallpox vaccination in the current era, including generalized vaccinia, progressive vaccinia, and eczema vaccinatum, appear to be rare (see References: Vellozzi 2005).

Risk of Contact Vaccinia

Contact vaccinia refers to transmission of vaccinia virus from newly vaccinated persons to susceptible unvaccinated contacts. Several past studies have examined the risk of contact vaccinia in the United States:

Statewide surveys conducted in 1963 and 1968 demonstrated that the risks of eczema vaccinatum in contacts of vaccinated persons were 16.8 and 20.0 per million primary vaccinations, respectively (see References: Lane 1970, Neff 1967). In the 1968 statewide surveys, the risk of accidental contact infections (other than eczema vaccinatum) was 44.6 per million primary vaccinations (see References: Lane 1970).
National surveys conducted during the same time period found somewhat lower rates for contact eczema vaccinatum (8.7 and 10.7 per million primary vaccinations) and for accidental contact infectious (3.5 and 7.9 per million primary vaccinations) but these surveys probably missed many less severe infections (see References: Neff 2002).
All studies conducted in the 1960s relied on appropriate recognition and reporting of contact cases; therefore, the data generated may not necessarily have reflected the true incidence of this condition.

A recent report has suggested that the risk may be somewhat higher than that observed in the 1960s for the following reasons (see References: Neff 2002):

Most members of the population are not immune to smallpox (nonimmune persons shed more virus when vaccinated than those who have some immunity).
A higher proportion of the current population has atopic dermatitis (particularly children).
A higher proportion of the current population has HIV infection or other immunosuppressive condition.

Nosocomial spread of vaccinia virus can occur, as summarized in a recent review article (see References: Sepkowitz 2003). However, among 27,700 healthcare workers vaccinated recently, no worker-to-patient transmission of vaccinia has occurred (see References: DoD 2007).

A 2004 study demonstrated that use of two occlusive dressings (an initial waterproof gauze-impregnated transparent bandage and an outer waterproof semipermeable bandage) to cover vaccination sites offered an excellent barrier against inadvertent transmission of vaccinia virus (see References: Talbot 2004). Treatment of the vaccination site with povidone iodine ointment, beginning 7 days after transcutaneous smallpox vaccination, appears to reduce the risks of autoinoculation or contact spread (see References: Hammarlund 2008).

Treatment of Vaccine Adverse Reactions

Therapies for adverse reactions to smallpox vaccination include vaccinia immunoglobulin (VIG), cidofovir (a nucleotide analogue of cytosine), and topical ophthalmic antiviral drugs for ocular involvement. Detailed information on use of these agents can be found in CDC: Smallpox vaccination and adverse reactions: guidance for clinicians (see References).

VIG is the primary product available to treat complications of vaccinia vaccination. VIG can be obtained by contacting the CDC Drug Service (see References: CDC: Drug Service), VIG is a sterile liquid immunoglobulin G (IgG) obtained from immunized donors. Two intravenous forms of VIG were approved by the FDA in February 2005 to treat patients in whom serious adverse reactions to smallpox vaccine develop, including the following (see References: FDA: VIGIV: Product approval information; Wittek 2006):

Aberrant infections induced by vaccinia virus that include its accidental implantation in eyes (except in cases of isolated keratitis), mouth, or other areas where vaccinia infection would constitute a special hazard
Eczema vaccinatum
Progressive vaccinia
Severe generalized vaccinia
Vaccinia infections in individuals who have skin conditions such as burns, impetigo, varicella-zoster, or poison ivy; or in individuals who have eczematous skin lesions because of either the activity or extensiveness of such lesions

Cidofovir may be used under an IND protocol to treat serious smallpox vaccine reactions (see References: CDC: Smallpox vaccination and adverse reactions: guidance for clinicians; CDC: Medical management of smallpox (vaccinia) vaccine adverse reactions). The proposed dose is 5 mg/kg administered intravenously, one time, over a 60-minute period; however, cidofovir should be administered in consultation with experts from CDC or the Department of Defense. CDC will supply cidofovir at no cost for use under the IND. Cidofovir will be released by CDC in the following situations:

A patient fails to respond to VIG
A patient is near death
All inventories of VIG have been exhausted

Off-label use of topical ophthalmic antiviral agents (trifluridine or vidarabine) has been recommended by some ophthalmologists to treat vaccinia infection of the conjunctiva or cornea.

Liability Issues Following Smallpox Vaccine Administration

The Homeland Security Act of 2002 (Section 304) addresses issues regarding liability following smallpox vaccination (see References: Homeland Security Act of 2002; CDC: Smallpox questions and answers: Section 304 of the Homeland Security Act).

Key points from Section 304, which went into effect in January 2003, include the following:

Section 304 applies to:

Smallpox vaccine manufacturers
Healthcare institutions and public health agencies that distribute vaccine or that administer smallpox vaccination programs
Licensed healthcare providers or other individuals authorized to administer smallpox vaccine or other smallpox countermeasures under state law
Any official, agent, or employee of the above entities

Section 304 states that no claim for liability for injury or death attributable to smallpox countermeasures, including vaccination or other substances used to treat or prevent smallpox, can be brought against the entities or individuals who are covered under the section, unless gross negligence, recklessness, illegal conduct, or willful misconduct can be demonstrated.

In April 2003, President Bush signed into law the Smallpox Emergency Personnel Protection Act of 2003. The law established a no-fault program to provide benefits and compensation to certain individuals (ie, healthcare workers and emergency responders) who are injured as a result of administration of smallpox vaccination or other smallpox countermeasures (see References: Smallpox Emergency Personnel Protection Act of 2003). A final rule for smallpox vaccine injury compensation was published in May 2006 in the Federal Register (see References: HHS: Final rule for smallpox vaccine injury compensation program). The new rule clarifies eligibility standards, the process for requesting and receiving benefits, and other policies and procedures.

Infection Control

Isolation Precautions

Airborne and Contact Precautions in addition to Standard Precautions should be implemented for patients with suspected smallpox.

Airborne Precautions:

Place the patient in a private room with negative air-pressure ventilation (minimum 6 air exchanges/hr).
Use external air exhaust or high-efficiency particulate air (HEPA) filters if the air is recirculated.
Keep the door to the room closed.

Contact Precautions:

Place the patient in a private room if available.
If a private room is not available, place the patient in a room with a patient who has active infection with the same organism (ie, cohort patients with smallpox).
Wear gloves when entering the room, change gloves after having contact with infectious material, remove gloves before leaving the room, and immediately wash hands using an antimicrobial agent.
Wear a gown when entering the room if clothing will have significant patient contact; remove the gown before leaving the room.
Move and transport the patient for essential purposes only. If transport is necessary, a mask should be placed on the patient.
When possible, dedicate the use of noncritical patient-care equipment.

Vaccination of Healthcare Workers

All healthcare workers caring for patients with suspected smallpox should be vaccinated immediately.

Cleaning and Disinfection of Environmental Surfaces

No disinfectant products are registered by the US Environmental Protection Agency (EPA) specifically for variola virus inactivation; however, according to CDC, products that inactivate similar lipid or medium-sized viruses (such as vaccinia virus) are adequate for disinfection of variola virus (see References: CDC: Smallpox response plan and guidelines, Guide F). These products include chemicals used on environmental surfaces for low- or intermediate-level disinfection and are outlined in the table below. High-level disinfectants or liquid chemical sterilants are not indicated for cleaning large environmental surfaces (eg, floors, walls, tabletops).

Chemicals Used on Environmental Surfaces for Low- or Intermediate-Level Disinfection
Disinfectant	Minimum Concentration to Achieve Inactivation
Ethyl alcohol	40%
Isopropyl alcohol	40%
Benzalkonium chloride	100 ppm
Sodium hypochlorite	200 ppm
Ortho-phenylphenol	40%
Iodophor	75 ppm
Abbreviation: ppm, parts per million.

Disinfection/Sterilization of Reusable Medical Equipment

Standard disinfection/sterilization methods approved by the FDA for medical instruments and devices are considered adequate for medical equipment used on smallpox patients, according to Guide F of the CDC Smallpox Response Plan (see References: CDC: Smallpox response plan and guidelines; Rutala 1996).

Laundry and Waste

Guide F of the CDC Smallpox Response Plan also outlines the following recommendations for management of textiles and fabrics:

Items should be handled with a minimum amount of agitation to avoid contamination of air, surfaces, and persons.
Textiles and fabrics (including clothing) should be bagged at the point of use in accordance with Occupational Safety and Health Administration (OSHA) regulations. Laundry should be labeled to indicate that laundry staff should wear appropriate personal protective equipment (as specified by OSHA rules on exposure to bloodborne pathogens).
Laundry can be washed using routine protocols for healthcare facilities (ie, hot water [71ºC or 160ºF] with detergent, bleach, and hot air drying)

The Working Group on Civilian Biodefense recommends that bedding and clothing of smallpox patients should be autoclaved or laundered in hot water to which bleach has been added (see References: Henderson: Smallpox as a biological weapon).

Decontamination of Air Space

Laboratory dispersion studies involving vaccinia virus indicate that infectious virions are rapidly inactivated in the environment (see References: CDC: Smallpox response plan and guidelines, Guide F). In one study, only 10% to 30% of viable variola viruses were recovered from controlled aerosols after 1 hour (see References: Mayhew 1970). Therefore, there is no evidence to support air space decontamination of rooms, facilities, or vehicles (eg, fumigation). Standard terminal cleaning practices are considered adequate for rooms that have housed smallpox patients.

Issues Related to Autopsies and Burial

Autopsy Practices

Recent guidelines from CDC indicate that Standard Precautions should be used for postmortem care. These include using a surgical scrub suit, surgical cap, impervious gown or apron with full sleeve coverage, a form of eye protection (eg, goggles or face shield), shoe covers, and double surgical gloves with an interposed layer of cut-proof synthetic mesh (see References: CDC: Medical examiners, coroners, and biologic terrorism: a guidebook for surveillance and case management).
In addition, autopsy personnel should wear N-95 respirators during all autopsies, regardless of suspected or known pathogens. Powered air-purifying respirators (PAPRs) equipped with N-95 or high-efficiency particulate air (HEPA) filters should be considered.

Burial

Contact with corpses should be limited to trained personnel and routine precautions should be implemented when transporting corpses.
Bodies contaminated with smallpox should be cremated without embalming. If cremation is not possible, bodies should be "properly secured in a sealed container (eg, a Zigler cases or other hermetically sealed casket) to reduce the potential risk of pathogen transmission" (see References: CDC: Medical examiners, coroners, and biologic terrorism: a guidebook for surveillance and case management).
An example of the type of system that can be used to seal remains prior to placing them in a casket for burial is the Bioseal system, produced by Barrier Products (see References). This system utilizes a polyaluminum foil–extruded laminate material that when used with a heat sealer will provide Level 1 containment for all gases, fluids, vapors, and odors associated with the transport and storage of human and animal remains.
According to WHO, "Cadavers should be cremated, in a properly designed facility, whenever possible and all persons coming in contact with them should be vaccinated or at least placed on daily fever watch. Body bags treated with hypochlorite bleach can also be used" (see References: WHO: Fact sheet on smallpox).

Public Health Reporting and Case Definitions

A case of smallpox is considered a public health emergency; therefore, any patients with a likely diagnosis of smallpox should be reported immediately to the state or local health department, according to disease reporting rules. Most states now have surveillance requirements and other components of a surveillance system in place (see References: CDC: Public health surveillance for smallpox).

Case definitions are as follows (see References: CDC: Smallpox response plan and guidelines: Guide A).

Clinical case definition:

An illness with acute-onset fever of 101°F (38.3°C) or more followed by a rash characterized by vesicles or firm pustules in the same stage of development without other apparent cause.

Laboratory criteria for confirmation:

Isolation of smallpox (variola) virus from a clinical specimen (LRN national laboratory) or
PCR identification of variola DNA in a clinical specimen
In the absence of smallpox cases (pre-event), the positive predictive value of smallpox-specific laboratory tests is low. Such testing should be reserved for cases that meet the CDC case definition for high risk of smallpox.

Case classification:

Confirmed: A case of smallpox that is laboratory-confirmed, or a case that meets the clinical case definition that is epidemiologically linked to a laboratory-confirmed case
Probable: A case that meets the clinical case definition, or a case that does not meet the clinical case definition but is clinically consistent with smallpox and has an epidemiologic link to a confirmed case of smallpox; examples of clinical presentations of smallpox that would not meet the ordinary type (pre-event) clinical case definition are: (a) hemorrhagic type, (b) flat type, and (c) variola sine eruptione
Suspect: A case with a febrile rash illness with fever preceding development of rash by 1 to 4 days

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