The effectiveness of the vaccine against influenza A(H1N1)pdm09-related illness during 2015 to 2016 seems to have been influenced by early exposure to specific influenza A (H1N1) viruses and the age at which individuals were exposed, according to data from the Influenza Vaccine Effectiveness Network. Comparing data from 2010-2011 and 2015-2016, investigators looked at birth cohorts to determine if they affected vaccine effectiveness. They found:
- The vaccine was 61% effective against A(H1N1)pdm09 illness during 2010-2011 through 2013-2014 seasons.
- Vaccine effectiveness was only 47% during 2015-2016.
- During the 2015-2016 season, in adults who were born from 1958 to 1979, it was only 22% effective, compared to 61% effectiveness in all other age groups combined.
Flannery B, Smith C, Garten RJ, et al. Influence of birth cohort on effectiveness of 2015–2016 influenza vaccine against medically attended illness due to 2009 pandemic influenza A(H1N1) virus in the United States. [Published online ahead of print January 18, 2018]. J Infect Dis. doi:10.1093/infdis/jix634.
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