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%â¯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.
Subject(s)
COVID-19 , Influenza Vaccines , Influenza, Human , Canada/epidemiology , Humans , Influenza A Virus, H3N2 Subtype , Influenza, Human/epidemiology , Influenza, Human/prevention & control , Pandemics/prevention & control , Vaccine EfficacySubject(s)
Mass Screening , Preventive Health Services , Humans , Research , Surveys and QuestionnairesABSTRACT
Influenza vaccine effectiveness against influenza and noninfluenza respiratory viruses (NIRVs) was assessed by test-negative design using historic datasets of the community-based Canadian Sentinel Practitioner Surveillance Network, spanning 2010-2011 to 2016-2017. Vaccine significantly reduced the risk of influenza illness by >40% with no effect on coronaviruses or other NIRV risk.