75% Of Canadians had SARS2 immunity due to infection

Canadian researchers have determined that since November 2021 through March 2023, three quarters of all Canadians had developed some immunity to SARS-COV-2, the virus that causes COVID-19. By November 2021, only 9% showed immunity. “The Evolution of SARS-CoV-2 Seroprevalence in Canada – A Time-Series Study, 2020-2023”. (CMAJ 2023 August 14;195:E1030-7. doi: 10.1503/cmaj.230949)

Tbis data is the result of research by the Public Health Agency of Canada and its COVID-19 Immunity Task Force (CITF).

The Canadian collaborating study teams were from: Action to beat Coronavirus Study (St. Michael’s Hospital, a site of Unity Health Toronto), Alberta Precision Laboratories, Cadham Provincial Laboratory, Canadian Blood Services, CanPath, Héma-Québec, Mount Sinai/Lunenfeld-Tanenbaum Research Institute, Saskatchewan Health Authority, University of Ottawa.

On 8/8/2023, 1,546 Canadians were hospitalized due to serious COVID-19 sickness. The case numbers have started to rise in the USA and in Canada due to a new variant. The numbers are not yet alarming say experts. See current data.

Today, 14 August 2023, the COVID-19 Immunity Task Force (CITF) published a comprehensive peer-reviewed analysis of pan-Canadian seroprevalence estimates in CMAJ (Canadian Medical Association Journal).

CITF Says more than 75% of Canadians had immunity to SARS-CoV-2 due to infection by March 2023. This supports the Civil Society Solidarity Partners against COVID-19 and IHME estimates of total infections in Canada and around the world versus reported data.

“Despite high vaccine coverage in Canada, the rate of infection rose rapidly with the highly contagious Omicron variant,” explains Dr. Bruce Mazer, study co-lead, Associate Scientific Director, Strategy at the CITF and Senior Scientist at the Research Institute of the McGill University Health Centre. “After six months with the Omicron variant circulating in Canada, in mid-June 2022, infection-acquired seroprevalence had risen to 47%, with an average monthly increase of 6.4% per month. It ultimately reached over 75% by March 2023.”


CITF March 2023
CITF funds diverse categories of SARS-CoV-2 research across Canada from basic immune science to vaccine surveillance. This pie chart gives a basic overview of the number of studies CITF are funding per category, although several studies straddle multiple categories.

“During Omicron, rates of infection-acquired immunity increased faster in younger age groups and in the Western provinces of Manitoba, Saskatchewan, Alberta, and British Columbia,” adds study co-lead Dr. David Buckeridge, Scientific Lead, Data Management & Analysis at the CITF and Professor, School of Population and Global Health, McGill University. “By March 2023, roughly 80% of adults aged 18-25 had evidence of a previous infection. That’s compared to approximately 75% of those aged 25-39 years, 70% of those aged 40-59 years, and 60% of those 60 and over.”

15 Jul 2024 COVID-19 Data for Canada from Civil Society Solidarity Partners against COVID-19  (CSPaC)

Source:  Civil Society Solidarity Partners against COVID-19