What is Vaccine, Influenza?

A killed virus vaccine. Both whole virion and subvirion vaccines are available. The composition of the vaccine is changed each year in response to antigenic shifts and changes in prevalence of influenza virus strains. The vaccine is usually bivalent or trivalent, containing one or two influenza virus A strains and one influenza virus B strain. Annual immunization before November is recommended for high-risk individuals (persons over 65 years of age and persons with chronic disease). (Dorland, 28th ed)