Influenza Vaccine Effectiveness
The trivalent influenza vaccines licensed in the United States for 2015 to 2016 contain hemagglutinin (HA) derived from an influenza A H1N1-like virus (A/California/7/2009), an influenza A H3N2-like virus (A/Switzerland/9715293/2013) and an influenza B virus (B/Phuket/3073/2013-like Yamagata lineage). This vaccine composition has a different influenza A H3N2 and influenza B antigenic composition than the vaccine offered during the 2014-2015 influenza season. Quadrivalent influenza vaccines contain these vaccine viruses, and another influenza B virus (B/Brisbane/60/2008-like Victoria lineage) virus (MMWR August 7, 2015 / 64(30);818-825).
The 2014-2015 influenza vaccine was effective only 50% of the time due to a mismatch between viral antigens included in the vaccine and viruses circulating in the community during flu season. The most recent report from CDC suggests that the 2015-2016 vaccine should be more effective against the influenza viruses that have been circulating in the United States and other countries (MMWR September 18, 2015 / 64(36);1011-1016)
Influenza outbreaks can happen as early as October and can last as late as May. Vaccination should begin in October before onset of community-wide influenza activity. Routine annual influenza vaccination is recommended for all individuals 6 months and older who do not have contraindications. Vaccination should continue to be offered as long as influenza viruses are circulating.
Immunity against influenza is short-lived. Antibody levels induced by influenza vaccine begin to decline within 6 months after vaccination, especially in individuals who are 65 years or older.
