FluWatch annual report: 2021–2022 influenza season
Following a season of sporadic influenza activity in 2020-2021, community circulation of seasonal influenza returned to Canada during the 2021–2022 influenza season. The Canadian seasonal influenza epidemic began in mid-April 2022 and ended in mid-June 2022 (epidemiological week 16 to 25). This influenza epidemic began exceptionally late in the season, and was exceptionally short in length and low in intensity.
During the 2021–2022 influenza season, 16,126 laboratory-confirmed influenza detections were reported out of 751,900 total laboratory tests. Far fewer detections were reported compared to pre-pandemic seasons despite elevated testing levels.
Nearly all of the detections were influenza A (99%) and the influenza A(H3N2) subtype predominated, accounting for 98% of subtyped influenza A specimens.
Considerable geographic variation was observed, as the majority of detections were recorded in Québec (47%), Alberta (17%), and British Columbia (10%).
Detailed information on age and influenza type/subtype was received for 14,159 laboratory-confirmed influenza detections, of which 49% were among individuals aged 0–19 years.
Nearly half of influenza A(H3N2) detections (46%) were among individuals aged 0–19 years, a much younger A(H3N2) case distribution than recorded in pre-pandemic seasons.
Of the 91 laboratory-confirmed influenza outbreaks reported this season, 49% were in long-term care facilities. Far fewer outbreaks were reported and a lower proportion occurred in long-term care facilities compared to recent pre-pandemic seasons.
Nearly all of the 776 influenza-associated hospitalizations reported by participating provinces and territories this season were influenza A (99.6%). Among hospitalizations with subtype information, 99.5% were associated with influenza A(H3N2). The annual seasonal hospitalization incidence was nine hospitalizations per 100,000 population, much lower than rates recorded in pre-pandemic seasons (average 42 hospitalizations per 100,000 population).
Influenza vaccine coverage in the 2021–2022 season was similar to the previous season. Coverage was estimated at 30% for adults aged 18 to 64 years and 71% among seniors (65 and older).
The Canadian Sentinel Practitioner Surveillance Network (SPSN) assessed 2021–2022 vaccine effectiveness (VE) against medically-attended influenza illness; vaccine effectiveness was estimated to be 36% against influenza A(H3N2), very similar to estimates obtained in other countries.
