Low influenza vaccine effectiveness against A(H3N2) associated hospitalizations in the 2016-2017 and 2017-2018 seasons of the Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN).


We evaluated vaccine effectiveness (VE) against hospitalization in the test-negative HAIVEN study. Nasal-throat swabs were tested by RT-PCR for influenza and VE was determined based on odds of vaccination by generalized estimating equations. Vaccine-specific antibody was measured in a subset of enrollees.

The 2016-2017 and 2017-2018 influenza seasons were notable for high number of hospitalizations for influenza A(H3N2) despite vaccine and circulating strain match.

Low VE for the A/Hong Kong/4801/2014 vaccine virus in both A(H3N2) seasons emphasizes concerns for continued changes in H3N2 antigenic epitopes, including changes that may impact glycosylation and ultimately reduce VE.

A total of 6,129 adults were enrolled from ten hospitals. Adjusted VE against A(H3N2) was 22.8% (95% C.I. 8.3%, 35.0%), pooled across both years and 49.4% (95% C.I. 34.3%, 61.1%) against B/Yamagata. In 2017-2018, the A(H3N2) VE point estimate for the cell-based vaccine was 43.0% (95% C.I. -36.3%, 76.1%; 56 vaccine recipients) compared to 24.0% (95% C.I. 3.9%, 39.9%) for egg based vaccines. Among 643 with serology data, hemagglutinin antibodies against the egg-based A(H3N2) vaccine strain were increased in influenza-negative individuals.

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