According to the Centers for Disease Control and Prevention (CDC), getting a seasonal flu shot can reduce your risk of flu by up to 90 percent. Flu shots confer protection against three influenza viruses: influenza A H3N2, influenza A H1N1 and influenza B. Specific strains are selected each year by experts at the Food and Drug Administration, based on surveillance data collected by World Health Organization laboratories.
Influenza A H3N2
Influenza A viruses are broken down into subtypes based on two surface proteins, hemagglutinin (H) and neuraminidase (N). The CDC has identified 16 different H and 9 different N proteins. One of the most common disease-producing combinations is H3N2. H3N2 strains selected for the seasonal flu shot in recent years include influenza A/Perth/16/2009 H3N2 (2010-2011), A/Brisbane/10/2007 H3N2 (2009-2010 and 2008-2009) and A/Wisconsin/67/2005 H3N2 (2007-2008).
Influenza A H1N1
Another subtype commonly implicated in human infections is H1N1. According to the FDA, recent H1N1 strains selected for the seasonal flu shot include A/California/7/09 H1N1 (2010-2011), A/Brisbane/59/2007 H1N1 (2009-2010 and 2008-2009) and A/Solomon Islands/3/2006 H1N1 (2007-2008). For the 2009-2010 flu season, the FDA approved a second, supplemental flu vaccine when a new and potentially dangerous H1N1 strain emerged in March 2009, after production of the seasonal flu vaccine was already underway. For the 2010-2011 flu season, the seasonal flu shot provides protection against the new H1N1 strain.
Influenza B
One influenza B virus is also included in the seasonal flu shot. Although, clinically, according to "Harrison's Principles of Internal Medicine," infections produced by influenza A and B viruses are indistinguishable, influenza B viruses mutate less frequently and are not divided into subtypes. In recent years, influenza B viruses selected for the seasonal flu shot have included B/Brisbane/60/2008 (2010-2011 and 2009-2010), B/Florida/4/2006 (2008-2009) and B/Malaysia/2506/2004 (2007-2008).
References
- CDC: Selecting the Viruses in the Seasonal Influenza (Flu) Vaccine
- FDA: Influenza Virus Vaccine Composition and Lot Release
- "Harrison's Principles of Internal Medicine, 17th edition;" A.S. Fauci, E. Braunwald, D.L. Kasper, S.L. Hauser, D.L. Longer, J.L. Jameson and J. Loscalzo (Eds.); 2008
