Inactivated Vaccine for Influenza A and

Each year s influenza vaccine contains three virus strains (usually two type A and one type B) representing the influenza viruses that are likely to circulate in the northern hemisphere during the upcoming winter (17). The vaccine is made from highly purified, egg-grown viruses that have been made noninfec-tious (inactivated). Whole-virus, subvirion, and purified surface-antigen preparations are available. 

Influenza vaccine is strongly recommended for any person aged 6 months or older, who—because of age or underlying medical condition—is at increased 

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Although the current influenza vaccine can contain one or more of the antigens administered in previous years, annual vaccination with the current vaccine is necessary because immunity declines in the year following vaccination. Because the previous year s vaccine differs from the current vaccine each year, supplies of vaccine from prior years should not be administered to provide protection for the current influenza season. 

Two doses administered at least 1 month apart may be required for satisfactory antibody responses among previously unvaccinated children younger than 9 years old however, studies of vaccines similar to those being used currently have indicated little or no improvement in antibody response when a second dose is administered to adults during the same season (73,78). 

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