The flu vaccine last season was almost completely ineffective at preventing the disease, but it might have helped some people stay out of the hospital, according to research reported at IDWeek 2015.
Overall, the vaccine failed to match the main circulating strain of influenza A, which in 2014-15 was an H3N2 virus, according to Alicia Fry, MD, of the CDC’s influenza division in Atlanta.
The vaccine strain of H3N2 was dubbed 3C.1, but starting in March it became clear that more than half of the circulating virus was of the types known as 3C.2a and 3C.3a — variants that were “low reactors” to the vaccine, she said.
By the time flu season was in full swing — October through December — more than three-quarters of the circulating H3N2 was of the 3C.2a variety, Fry reported. Although there was some variation from state to state, only a few regions had substantial amounts of “vaccine-like” virus.
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