Influenza vaccine

[Raeanne Dimick]

The influenza virus vaccine helps protect against influenza. Two types of influenza virus, type A and type B, regularly cause seasonal epidemics of influenza in the United States. There are many different strains within each type. The strains of virus that cause influenza outbreaks change each year. Thus, a new vaccine is needed each year. Each year

[Jessica]

Based on recommendations by the World Health Organization and the Centers for Disease Control and Prevention (CDC), vaccines for influenza are modified annually to include the most prevalent strains (usually 2 strains of influenza A and 1 or 2 strains of influenza B). Sometimes slightly different vaccines are used in the northern and southern hemispheres.
For more information, see Influenza Advisory Committee on Immunization Practices Vaccine Recommendations and CDC: Influenza Vaccination.
(See also Overview of Immunization.)