SILVER SPRING, Md. — The Food and Drug Administration has approved what it called the first flu vaccine to prevent four strains of the influenza virus.

The agency announced Wednesday the approval of MedImmune's FluMist Quadrivalent, which contains two influenza A and two influenza B strains. The currently approved version of FluMist is trivalent, containing two influenza A strains and one B strain, as are the other FDA-approved vaccines. The FDA said that in any given year, there may be two influenza B strains, or the strain in the vaccine may not be the one circulating.

"Illness caused by influenza B virus affects children, particularly young and school-aged, more than any other population," FDA Center for Biologics Evaluation and Research director Karen Midthun said. "A vaccine containing the four virus strains most likely to spread and cause illness during the influenza season offers an additional option to aid in influenza prevention efforts."

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