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.
