Vaccine effectiveness 45 percent for flu virus linked to ARI

The overall vaccine effectiveness (VE) against any influenza virus associated with medically attended acute respiratory illness (ARI) is 45 percent for the current influenza season, according to research published in the Feb. 21 issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Fatimah S. Dawood, M.D., from the CDC in Atlanta, and colleagues used data from 4,112 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network during Oct. 23, 2019, to Jan. 25, 2020, to develop an interim report on influenza vaccine effectiveness for preventing laboratory-confirmed influenza.

The researchers found that VE was 45 percent against any influenza virus associated with medically attended ARI. VE was estimated to be 50 and 37 percent against influenza B/Victoria viruses and influenza A(H1N1)pdm09, respectively. Among children and adolescents aged 6 months to 17 years, vaccination provided substantial protection (VE, 55 percent). The interim estimates were consistent with those from previous seasons and varied from 40 to 60 percent when influenza vaccines were matched antigenically with circulating viruses.

"This season, influenza B and A(H1N1)pdm09 viruses have cocirculated, and influenza activity remains elevated in most parts of the country," the authors write. "Interim VE estimates indicate that the current season's influenza vaccine reduces the risk of medical visits associated with influenza, including visits associated with circulating influenza B viruses."

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