Influenza Virus Vaccine Composition and Lot Release

Each year, experts from the FDA, WHO, U.S. Centers for Disease Control and Prevention (CDC), and other institutions study virus samples and patterns collected from around the world in an effort to identify strains that may cause the most illness in the upcoming season.  Based on those forecasts and on the recommendations of the FDA’s Vaccine and Related Products Advisory Committee, the FDA determines the three strains that manufacturers should include in their vaccines for the U.S. population. The closer the match between the circulating strains and the strains in the vaccine, the better the protection against the disease.