Most Americans Who Got This Season's Flu Shot Could Get Sick Anyway

More than three-quarters of Americans who got this season’s flu shot could get the virus anyway, given a mismatch between the flu strains covered by the shot and those actually causing illness in people, U.S. officials said.

An interim CDC report found the shot was only 23 percent effective overall, a performance about in line with what the U.S. Centers for Disease Control and Prevention predicted last year, experts said. At the time, CDC warned that the predominant flu virus, influenza A (H3N2), had “drifted” or changed genetically since the shot was made.

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