Each year, influenza experts from the FDA, World Health Organization, the Centers for Disease Control and Prevention and others in the public health field study virus samples and patterns collected worldwide to identify virus strains likely to cause the most illness in upcoming influenza season.
Based on that information and the recommendations of the FDA's Vaccines and Related Biological Products Advisory Committee, the strains selected for the 2011/2012 influenza season are:
-- A/California/7/09 (H1N1)-like virus (pandemic (H1N1) 2009 influenza virus).
-- A/Perth /16/2009 (H3N2)-like virus.
-- B/Brisbane/60/2008-like virus.
There is always a possibility of a less than optimal match between the virus strains predicted to circulate and the virus strains that end up causing the most illness, but even if there is not an exact match, the vaccine may reduce the severity or help reduce complications, health officials say.
"Vaccines to prevent seasonal influenza have a long and successful track record of safety and effectiveness in the United States," Dr. Karen Midthun, director of FDA's Center for Biologics Evaluation and Research, says in a statement.
"It is important to get vaccinated every year, even if the strains in the vaccine do not change, because the protection received the previous year will diminish over time and may be too low to provide protection into the next year."