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@NEJM Ask the Authors & Experts: Influenza Vaccine Effectiveness in the United States — 2015/16 Season

Original Article

Influenza Vaccine Effectiveness in the United States — 2015/16 Season

Michael L. Jackson, PhD; Jessie R. Chung, MPH; Lisa A. Jackson, MD; C. Hallie Phillips, MEd; Joyce Benoit, BSN; Arnold S. Monto, MD; Emily T. Martin, PhD; Edward A. Belongia, MD; Huong Q. McLean, PhD; Manjusha Gaglani, MD; Kempapura Murthy, MPH; Richard Zimmerman, MD; Mary Patricia Nowalk, PhD; Alicia M. Fry, MD; Brendan Flannery, PhD

August 26, 2017.


The A(H1N1)pdm09 virus strain used in live attenuated influenza vaccine (LAIV) was changed for the 2015/16 influenza season, due to lack of effectiveness in young children in 2013/14. The United States Influenza Vaccine Effectiveness Network evaluated the impact of this change as part of our estimates of influenza vaccine effectiveness in 2015/16.

We enrolled patients aged ≥6 months seeking care for acute respiratory illness at ambulatory care clinics in geographically diverse US sites. We estimated vaccine effectiveness using a test-negative design, comparing the odds of testing positive for influenza among vaccinated vs. unvaccinated participants, with separate estimates for inactivated influenza vaccines (IIV) and LAIV.

Among 6,879 eligible participants, 1,309 (19%) tested positive for influenza, predominantly A(H1N1)pdm09 (11%) and influenza B (7%). Influenza vaccine effectiveness against any influenza illness was 48% (95% confidence interval (CI), 41 to 55%). Among children 2-17 years of age, IIV was 60% effective (95% CI, 47 to 70%), while LAIV was not observed to be effective (5%; 95% CI, -47 to 39%). Vaccine effectiveness against A(H1N1)pdm09 in children was 63% (95% CI, 45 to 75%) for IIV, compared to -19% (-113 to 33%) for LAIV.

Influenza vaccines reduced the risk of influenza illness in 2015/16. However, LAIV was found to be ineffective in children in a year with substantial IIV effectiveness. Because the 2016/17 LAIV A(H1N1)pdm09 vaccine strain was unchanged from 2015/16, the US Advisory Committee on Immunization Practices made an interim recommendation not to use LAIV for the 2016/17 influenza season.


 Originally Appeared in The New England Journal of Medicine on August 16, 2017.


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