Vaccination

Last updated December 16, 2010. At the current time, this content is considered historical and will not be updated until further notice.

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Vaccine Use in the United States During the 2009-2010 Season
Vaccine Efficacy
Global Production of pH1N1 Vaccine
CDC Vaccine Recommendations for the 2010-2011 Influenza Season

Vaccine Use in the United States During the 2009-2010 Season

On September 15, 2009, the FDA announced approval of four pH1N1 2009 influenza vaccines, and in November 2009 approved a fifth one. By October 9, 2009, all states had placed orders for the vaccine. Initially, the CDC's Advisory Committee on Immunization Practices (ACIP) recommended that vaccination efforts focus on five target groups of persons at high risk for influenza. These groups included:

• Pregnant women
• Persons who live with or provide care for infants younger than 6 months (eg, parents, siblings, and day-care providers)
• Healthcare and emergency medical services personnel
• Persons aged 6 months to 24 years
• Persons aged 25 to 64 who have medical conditions that put them at higher risk for influenza-related complications

As vaccine supply increased, restrictions to target groups were eased, and by late December 2009, vaccination became available to the general public (CDC: The 2009 H1N1 pandemic: summary highlights). By the end of 2009, approximately 61 million persons had been vaccinated in the United States, and by January 29, 2010, 124 million doses had been distributed. 

To estimate state-specific vaccination coverage for the 2009-2010 influenza season, the CDC analyzed results from the Behavioral Risk Factor Surveillance System and the National 2009 H1N1 Flu Survey for the period November 2009 through February 2010. Estimated state vaccination rates among persons 6 months of age and older ranged from 12.9% in Mississippi to 38.8% in Rhode Island. Median coverage was 36.8% for children 6 months to 17 years, 20.1% for adults 18 and over, and 33.2% for persons in the ACIP target groups (CDC 2010: Interim results: state-specific influenza A (H1N1) 2009 monovalent vaccination coverage).

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Vaccine Efficacy

Clinical studies of the 2009 H1N1 monovalent vaccines indicate that this vaccine antigen is immunogenic and response rates are similar to those observed after immunization with influenza A antigens found in typical seasonal influenza vaccines.

• Among children aged 6 to 35 months, 19% to 92% responded with a hemagglutination inhibition (HI) titer ≥40 at ≥21 days after one dose, and >90% responded with an HI titer ≥40 after two doses separated by ≥21 days (ACIP 2010, Nolan 2010).
• Among children aged 3 to 9 years, 44% to 93% responded with an HI titer ≥40 at 21 or more days after one dose, and >90% responded with an HI titer ≥40 after two doses separated by ≥21 days (ACIP 2010).
• In a study in the Republic of Korea, 118 subjects aged 6 months to <9 years and 130 subjects 9 years to <18 years were enrolled in a multicenter open label clinical trial. Subjects received either 7.5 mcg (subjects 6 months to <3 years of age) or 15 mcg (subjects 3 years to <18 years of age). By day 21 after the first dose, HI titers of >40 were observed in 6% of subjects 6 months to <3 years of age, 35% of subjects 3 to <9 years of age, and 81% of subjects 9 to 18 years of age. By day 21 after the second dose, the titers of >40 had been achieved by 56%, 70%, and 91% of the respective groups. The authors concluded that a single 15-mcg dose of vaccine was immunogenic in subjects 9 years of age or older. However, a two-dose regimen was needed to produce potentially protective antibody titers in younger children (Oh 2010).
• In a Taiwanese study, 183 healthy children and adolescents aged 1 year to 17 years received two doses of a monovalent, unadjuvanted, inactivated, split-virus vaccine. Three weeks after the first dose, 36% of children age 1 to 2, 53% of children age 3 to 5, 57% of children age 6 to 9, and 90% of children age 10 to 17 generated protective antibodies. A second vaccination given 3 weeks later induced protective antibodies in 89% of all age-groups (Lu 2010).
• In a multicenter, randomized laboratory-blinded clinical trial in Taiwan, 107 subjects aged 60 years or older (range 61 to 86 years), were randomized to receive 15 mcg or 30 mcg of hemagglutinin antigen (Kao 2010). At 3 weeks post-vaccination, an HI titer ³40 was observed in 76% in the 15-mcg group and 81% in the group receiving 30 mcg. This study indicated that one dose of 15 mcg of hemagglutinin antigen without adjuvant induced a protective immune response in the majority of elderly subjects.
• Among older children and adults, response rates after one dose of vaccine exceeded 90% (Greenberg 2009, Plennevaux 2010), although geometric mean titers were substantially lower among adults aged ≥50 years in one study (Greenberg 2009) and among adults aged ≥65 years (Plennevaux 2010).

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Global Production of pH1N1 Vaccine

The first commercially available pandemic influenza vaccines were registered for use in September of 2009, 5 months after identification of the pandemic H1N1 virus. The goal of the WHO's Global Pandemic Influenza Action Plan was to have enough vaccine to vaccinate two billion people with one dose within 6 months after industry had the vaccine prototype (WHO 2006).

The actual global production of pandemic vaccine by December 1, 2009, was 534 million doses, and the forecasted production of pandemic vaccine 12 months after the availability of the vaccine virus (ie, June 2010) was approximately 1.37 billion doses, which is only 28% of the annual global production capacity of 4.9 billion doses estimated from a WHO survey conducted in May 2009. Reasons cited for decreased production were (Partridge 2010):

• Lower-than-expected vaccine virus yields
• Inability of manufacturers to use their most dose-sparing formulations
• Reluctance of certain regulatory agencies to register adjuvanted low-antigen dose vaccine formulations
• Shrinking vaccine demand (due to the bulk of vaccine delivery coming after the fall wave had peaked and in the face of a pandemic of moderate severity)
• Stopping of pandemic vaccine production by some manufacturers in late 2009 and by almost all manufacturers in early 2010 to switch to Southern and Northern Hemisphere seasonal vaccine production, respectively

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CDC Vaccine Recommendations for the 2010-2011 Influenza Season

The vaccine for the 2010-2011 season protects against three influenza viruses, including the 2009 pandemic H1N1 virus. Virus strains in the 2010-2011 vaccine include:

• A/California/7/09 (H1N1)-like virus (pH1N1 2009 influenza virus)
• A/Perth/16/2009 (H3N2)-like virus
• B/Brisbane/60/2008-like virus

The CDC currently recommends annual seasonal influenza vaccination for all persons age 6 months and older (ACIP 2010).

When vaccine supply is limited, the CDC recommends that vaccination efforts should focus on delivering vaccination to (ACIP 2010):

• Children aged 6 months to 4 years (59 months)
• Adults aged ≥50 years
• Persons with chronic pulmonary (including asthma), car­diovascular (except hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus)
• Immunosuppressed persons (including immunosuppres­sion caused by medications or by human immuno­deficiency virus [HIV])
• Pregnant women
• Persons aged 6 months to 18 years and receiving long-term aspirin therapy and who therefore might be at risk for experiencing Reye's syndrome after influenza virus infection
• Residents of nursing homes and other chronic-care facilities
• American Indians/Alaska Natives
• Persons who are morbidly obese (body mass index ≥40)
• Healthcare personnel
• Household contacts and caregivers of children aged <5 years and adults aged ≥50 years, with par­ticular emphasis on vaccinating contacts of children aged <6 months
• Household contacts and caregivers of persons with medical conditions that put them at higher risk for severe complications from influenza

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