Influenza vaccine effectiveness against A(H3N2) during the delayed 2021/22 epidemic in Canada

Euro Surveill. 2022 Sep;27(38):2200720. doi: 10.2807/1560-7917.ES.2022.27.38.2200720.

Abstract

Influenza virus circulation virtually ceased in Canada during the COVID-19 pandemic, re-emerging with the relaxation of restrictions in spring 2022. Using a test-negative design, the Canadian Sentinel Practitioner Surveillance Network reports 2021/22 vaccine effectiveness of 36% (95% CI: -38 to 71) against late-season illness due to influenza A(H3N2) clade 3C.2a1b.2a.2 viruses, considered antigenically distinct from the 3C.2a1b.2a.1 vaccine strain. Findings reinforce the World Health Organization's decision to update the 2022/23 northern hemisphere vaccine to a more representative A(H3N2) clade 3C.2a1b.2a.2 strain.

Keywords: A(H3N2); Influenza; clade; observational study; test-negative design; vaccine effectiveness.

MeSH terms

  • COVID-19*
  • Canada / epidemiology
  • Humans
  • Influenza A Virus, H3N2 Subtype
  • Influenza Vaccines*
  • Influenza, Human* / epidemiology
  • Influenza, Human* / prevention & control
  • Pandemics / prevention & control
  • Vaccine Efficacy

Substances

  • Influenza Vaccines