Nov 27, 2001 (CIDRAP News) – If smallpox reappears in the United States, health authorities will strive to trace and vaccinate everyone who has had contact with infected or exposed persons but probably will not mount any mass vaccination campaigns, according to a draft plan released Monday by the Centers for Disease Control and Prevention (CDC).
This "ring vaccination" strategy is what succeeded in eradicating the disease in the 1970s, the CDC's Harold Margolis, MD, told reporters during a telephone briefing Monday. He explained, "At the heart of this plan is ring vaccination or what is sometimes called search and containment—that is, identifying infected individuals and locating those people who come in contact with that person and vaccinating those people in outward rings of contact. . . . This really produces a buffer zone of immune individuals and was shown to prevent smallpox and ultimately eradicate this disease."
Although federal officials are currently negotiating with drug companies for enough smallpox vaccine to inoculate every American, CDC officials said the "Interim Smallpox Response Plan and Guidelines" does not call for mass vaccination in the absence of any smallpox outbreak. A Nov 26 news release states, "The plan does not call for mass vaccination in advance of a smallpox outbreak because the risk of side effects from the vaccine outweigh[s] the risk of someone actually being exposed to the smallpox virus."
Further, the response plan indicates that the CDC is not likely to call for a regional or local mass vaccination program in response to an outbreak. The plan's executive summary cites several reasons that ring vaccination would be "more desirable than an indiscriminate mass vaccination campaign." These include the effectiveness of ring vaccination, the increased risk of adverse reactions in a mass campaign, the limited supply of vaccinia immune globulin (VIG) for treating patients suffering adverse reactions, and the limited current supply of vaccine itself. "Current supplies of smallpox vaccine would be exhausted quickly if an indiscriminate campaign was utilized," the summary states.
The smallpox response plan has been developed because of the fear that bioterrorists could obtain and release the smallpox virus, even though the disease was declared eradicated in 1980. The plan is described as a draft that is subject to continued modification, but it would be used if an outbreak occurred, according to the CDC. The document was sent to all state health departments Nov 23, Lisa Rotz, MD, a CDC bioterrorism preparedness specialist, said at Monday's briefing.
"We've been working on updating this plan from a plan that was originally developed in 1972 to deal with importations of smallpox, after we stopped vaccinating routinely here in the US," Rotz said. The plan summary says that, if the virus were reintroduced, it could spread more rapidly than it did in the past, for three reasons: very few people now have immunity, health personnel might be slow to recognize the disease, and today's population is more mobile and more crowded.
Rotz said the CDC could make smallpox vaccine available anywhere in the country within hours after being notified. The plan summary includes a priority list of groups who would be vaccinated in the case of an outbreak. Leading the list are close contacts of smallpox patients, followed by people exposed to the initial release of the virus (if identified early enough), household members of contacts, patients' medical care providers, laboratory personnel who handle specimens from patients, people involved in contact tracing or quarantine enforcement, and law enforcement personnel who interview suspected patients. The CDC director could decide to offer voluntary vaccination to other groups in support roles, including public health, emergency management, and law enforcement personnel.
The number of smallpox vaccine doses currently available in the United States is usually estimated at about 15 million. The possibility of diluting the vaccine to multiply the number of doses is currently being studied, and Donald A. Henderson, MD, said at Monday's briefing that early results indicate that the available doses can probably be diluted by a factor of 5 without sacrificing effectiveness.
"It looks very encouraging for 1 to 5, but with a little bit of a cushion for even 1 to 10," he said. "I think if a problem occurred today and we needed the vaccine, we'd be ready to go in 1 to 5 immediately." He said that in one study involving 77 individuals, the diluted vaccine induced a "take" in every case. Henderson, who led the smallpox eradication campaign in the 1960s and 1970s, is director of the Office of Public Health Preparedness in the federal Department of Health and Human Services (HHS).
The short supply of VIG is third on the plan's list of reasons for not doing mass vaccination campaigns. At Monday's briefing, Rotz said the CDC and the Department of Defense together have only enough VIG to treat about 600 adverse reactions. About one person per million vaccinated dies because of progressive vaccinia, postvaccinial encephalitis, or severe eczema vaccinatum, according to the plan summary.
In Monday's briefing, reporters pressed officials with questions about various types of smallpox exposure scenarios, such as an infected person going to a crowded baseball stadium or flying from New York to Los Angeles. Henderson explained that the disease has an incubation period of 10 to 12 days, during which the person "feels perfectly well and is not able to transmit infection." The person does not become infectious until he or she develops the rash, he said.
Henderson did not rule out the possibility of mass vaccination in a local area. "If you get a situation where, let's say, there are so many cases in a city that you can't do the contact tracing in the same way or as effectively or it's broader than that, you might very well . . . vaccinate the entire area, but you'd still try to keep putting more vaccine in the places where it's going to do the most good," he said.
In response to a question about how to predict the size of a smallpox outbreak, Henderson commented that the disease spreads much more easily in the winter. In cases of smallpox introduction in Europe between 1950 and 1972, he said, the disease was 5 to 10 times more likely to spread if it was introduced between November and April than was the case the rest of the year.
State and local health officials are being asked to evaluate the smallpox plan, identify any shortcomings they see, and examine how the plan fits with their own plans, CDC officials said.
CDC press release about the plan
Transcript of the CDC's Nov 26 press briefing on the plan