Author(s): Skowronski DM, Chambers C, Sabaiduc S, De Serres G, Winter AL,
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Abstract BACKGROUND: The 2014-2015 influenza season was distinguished by an epidemic of antigenically-drifted A(H3N2) viruses and vaccine components identical to 2013-2014. We report 2014-2015 vaccine effectiveness (VE) from Canada and explore contributing agent-host factors. METHODS: VE against laboratory-confirmed influenza was derived using a test-negative design among outpatients with influenza-like illness. Sequencing identified amino acid mutations at key antigenic sites of the viral hemagglutinin protein. RESULTS: Overall, 815/1930 (42\%) patients tested influenza-positive: 590 (72\%) influenza A and 226 (28\%) influenza B. Most influenza A viruses with known subtype were A(H3N2) (570/577; 99\%); 409/460 (89\%) sequenced viruses belonged to genetic clade 3C.2a and 39/460 (8\%) to clade 3C.3b. Dominant clade 3C.2a viruses bore the pivotal mutations F159Y (a cluster-transition position) and K160T (a predicted gain of glycosylation) compared to the mismatched clade 3C.1 vaccine. VE against A(H3N2) was -17\% (95\% confidence interval [CI], -50\% to 9\%) overall with clade-specific VE of -13\% (95\% CI, -51\% to 15\%) for clade 3C.2a but 52\% (95\% CI, -17\% to 80\%) for clade 3C.3b. VE against A(H3N2) was 53\% (95\% CI, 10\% to 75\%) for patients vaccinated in 2014-2015 only, significantly lower at -32\% (95\% CI, -75\% to 0\%) if also vaccinated in 2013-2014 and -54\% (95\% CI, -108\% to -14\%) if vaccinated each year since 2012-2013. VE against clade-mismatched B(Yamagata) viruses was 42\% (95\% CI, 10\% to 62\%) with less-pronounced reduction from prior vaccination compared to A(H3N2). CONCLUSIONS: Variation in the viral genome and negative effects of serial vaccination likely contributed to poor influenza vaccine performance in 2014-2015. © The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America.
This article was published in Clin Infect Dis
and referenced in Journal of Vaccines & Vaccination