Birth cohort affected 2015-2016 flu vaccine effectiveness

Early influenza encounters could influence vaccine response
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The influenza vaccine introduced in 2009 showed reduced effectiveness during the 2015-2016 influenza season, but only in adults born between 1958 and 1979, according to an analysis published online in the Journal of Infectious Diseases.

SOURCE: Flannery B et al. J Infect Dis. 2018 Jan 18. doi: 10.1093/infdis/jix634.

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This study proposes that influenza virus strains encountered early in life focus the immune response to later infection or vaccination on shared epitopes between the early and later strains. Supporting this hypothesis is evidence from other studies showing that 60% of the serological response to inactivated influenza vaccines is the result of boosting pre-existing antibodies, rather than the creation of new, vaccine-induced antibodies.

However there are also some flaws to this argument, and we should be careful to avoid confirmation bias. For example, the reduction in effectiveness of vaccines against A(H1N1) has been observed in North America, where this study is located, but to a lesser extent in studies conducted in other regions. Reductions in vaccine effectiveness have also been observed in other birth cohorts and during other influenza seasons.

That aside, accumulating evidence suggests that the vaccine strain be updated from A/California/7/2009 to A/Michigan/45/2015 (a clade 6B.1 strain) for the 2016-2017 influenza seasons.
 

Allen C. Cheng, PhD, is from the School of Public Health and Preventive Medicine at Monash University, Melbourne, and Kanta Subbarao, MBBS, is from the World Health Organization Collaborating Centre for Reference and Research on Influenza and the Peter Doherty Institute for Infection and Immunity, Australia. These comments are taken from an accompanying editorial (J Infect Dis. 2018, Jan 18. doi: 10.1093/infdis/jix635). The authors declared support from the Australian Department of Health and the Australian National Health and Medical Research Council. No conflicts of interest were declared.

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