N Engl J Med

Abstract

BACKGROUNDThe A(H1N1)pdm09 virus strain used in the live attenuated influenza vaccine was changed for the 2015\u20132016 influenza season because of its lack of effectiveness in young children in 2013\u20132014. The Influenza Vaccine Effectiveness Network evaluated the effect of this change as part of its estimates of influenza vaccine effectiveness in 2015\u20132016.METHODSWe enrolled patients 6 months of age or older who presented with acute respiratory illness at ambulatory care clinics in geographically diverse U.S. sites. Using a test-negative design, we estimated vaccine effectiveness as (1 \u2013 OR) 7 100, in which OR is the odds ratio for testing positive for influenza virus among vaccinated versus unvaccinated participants. Separate estimates were calculated for the inactivated vaccines and the live attenuated vaccine.RESULTSAmong 6879 eligible participants, 1309 (19%) tested positive for influenza virus, predominantly for A(H1N1)pdm09 (11%) and influenza B (7%). The effectiveness of the influenza vaccine against any influenza illness was 48% (95% confidence interval [CI], 41 to 55; P<0.001). Among children 2 to 17 years of age, the inactivated influenza vaccine was 60% effective (95% CI, 47 to 70; P<0.001), and the live attenuated vaccine was not observed to be effective (vaccine effectiveness, 5%; 95% CI, 1247 to 39; P = 0.80). Vaccine effectiveness against A(H1N1)pdm09 among children was 63% (95% CI, 45 to 75; P<0.001) for the inactivated vaccine, as compared with 1219% (95% CI, 12113 to 33; P = 0.55) for the live attenuated vaccine.CONCLUSIONSInfluenza vaccines reduced the risk of influenza illness in 2015\u20132016. However, the live attenuated vaccine was found to be ineffective among children in a year with substantial inactivated vaccine effectiveness. Because the 2016\u20132017 A(H1N1)pdm09 strain used in the live attenuated vaccine was unchanged from 2015\u20132016, the Advisory Committee on Immunization Practices made an interim recommendation not to use the live attenuated influenza vaccine for the 2016\u20132017 influenza season. (Funded by the Centers for Disease Control and Prevention and the National Institutes of Health.)20172018-02-10T00:00:00ZUL1 TR000005/TR/NCATS NIH HHS/United StatesUL1 RR024153/RR/NCRR NIH HHS/United StatesU01 IP000473/IP/NCIRD CDC HHS/United StatesU01 IP000466/IP/NCIRD CDC HHS/United StatesU01 IP000471/IP/NCIRD CDC HHS/United StatesU01 IP000474/IP/NCIRD CDC HHS/United StatesU01 IP000467/IP/NCIRD CDC HHS/United States28792867PMC5727917855