Influenza Vaccine Effectiveness in the United States During the 2016–2017 Season

Abstract

In recent influenza seasons, the effectiveness of inactivated influenza vaccines against circulating A(H3N2) virus has been lower than against A(H1N1)pdm09 and B viruses, even when circulating viruses remained antigenically similar to vaccine components. During the 2016–2017 influenza season, vaccine effectiveness (VE) across age groups and vaccine types was examined among outpatients with acute respiratory illness at 5 US sites using a test-negative design that compared the odds of vaccination among reverse transcription polymerase chain reaction–confirmed influenza positives and negatives. Among 7083 enrollees, 1342 (19%) tested positive for influenza A(H3N2), 648 (9%) were positive for influenza B (including B/Yamagata, n = 577) and 5040(71%) were influenza negative. Vaccine effectiveness was 40% (95% confidence interval [CI], 32% to 46%) against any influenza virus, 33% (95%CI, 23% to 41%) against influenza A(H3N2) viruses and 53% (95%CI, 43% to 61%) against influenza B viruses. The 2016–2017 influenza vaccines provided moderate protection against any influenza among outpatients, but were less protective against influenza A(H3N2) viruses than B viruses. Approaches to improving effectiveness against A(H3N2) viruses are needed.