Influenza Vaccine

Influenza vaccine contains inactivated influenza virus or viral components. The vaccine is given annually because its composition is changed year to year (in response to the continuing antigenic drift of influenza viruses) and because immunity is relatively short-lived. Since 1976, the influenza vaccine has been a trivalent product containing the 2 influenza A strains predominant during recent influenza seasons (H1N1 and H3N2) and an influenza B strain.

In the US, elderly people account for > 80% of all influenza-related deaths. About 90% of these deaths occur in people with recognized underlying high-risk conditions (eg, chronic pulmonary, cardiac, renal, or metabolic disorders), but some deaths occur in apparently healthy elderly people.

The vaccine should be given IM annually to all people >= 65. To reduce risk of spreading influenza, all health care practitioners caring for elderly people and all children living with elderly people should be immunized annually.

Vaccination, if done shortly before the anticipated influenza season (mid-October through mid-November in the Northern Hemisphere), reduces risk maximally; however, vaccination as late as January may still reduce risk to some degree, depending on when the season starts. Efficacy (about 75 to 80% in young adults) declines with aging, but even in the elderly, the vaccine is protective; it reduces the severity of illness, protects against serious complicating bacterial pneumonia, and reduces mortality risk.

A live attenuated influenza vaccine given intranasally, which is highly effective in younger people, is not recommended for use in the elderly.

This topic was last updated February 2006.