During the 2015-2016 season, influenza vaccines overall reduced the risk of influenza illness, but the live attenuated influenza vaccine (LAIV) was ineffective in children, according to a recently-published study.

Researchers from the Influenza Vaccine Effectiveness Network published their findings in the New England Journal of Medicine. For the study, the study researchers enrolled patients aged 6 months and older who presented with acute respiratory illness at study-site clinics during the 2015-16 flu season. To determine vaccine effectiveness, the researchers used a test-negative design to estimate effectiveness as the odds of testing positive for flu in both vaccinated and unvaccinated patients.

Of the 6,879 participants, 19% tested positive for influenza. Most of the flu illnesses included the 2009 H1N1 and influenza B strains. The researchers determined that, overall, the flu vaccine efficacy was 48%. In children aged 2-17 years old, the inactivated flu vaccine showed 60% effectiveness, but the researchers saw no effectiveness for the LAIV.

Since the 2016-2017 A(H1N1)pdm09 strain used in the LAIV was unchanged from the previous season, the Advisory Committee on Immunization Practices recommended against the use of the live attenuated influenza vaccine in its 2017 updated adult immunization recommendations.

Jackson ML, Chung JR, Jackson LA, et al. Influenza vaccine effective in the United States during the 2015-2016 season. N Engl J Med. 2017. 377:534-543. DOI: 10.1056/NEJMoa1700153