Canada’s Battle Against COVID-19: Three Quarters Immune by March 2023

COVID Update

In-depth Analysis from the COVID-19 Immunity Task Force Sheds Light on the Omicron Dominance and Immunity Landscape

Omicron’s Dominance: By March 2023, after 16 months of the Omicron variant’s rule, three out of every four Canadians gained immunity to SARS-CoV-2 due to infection. The comprehensive pan-Canadian seroprevalence analysis was made public by the COVID-19 Immunity Task Force (CITF) in the Canadian Medical Association Journal.

The Study’s Approach: Collaborating with seven distinguished teams of scientists, CITF delved deep into infection-derived and vaccine-induced antibody prevalence in Canada. Blood samples were meticulously dissected from:

  • Pre-vaccination era (March 2020 – November 2020)
  • Vaccine deployment phase (December 2020 – November 2021)
  • The Omicron reign (December 2021 – March 2023)

Pre-Omicron Infection Rates: Surprisingly, before Omicron’s surge, only a minor fraction of Canadians displayed any sign of previous SARS-CoV-2 infection. This was consistent with patterns observed in affluent nations in Europe and North America.

The Omicron Surge: The introduction of the highly transmissible Omicron variant caused a spike in infections. Dr. David Buckeridge, study co-lead and Professor at McGill University, remarks, “Despite Canada’s rigorous vaccination program, by March 2023, about 80% of adults between 18-25 years had evidence of a past infection.”

Present Trends and Forward Path: Although infection rates have plateaued since Spring 2023, the researchers emphasize that varying immunity levels across demographics and regions necessitate tailor-made public health and clinical measures.

Research Methodology: Researchers utilized nucleocapsid protein antibodies to identify past infections and anti-spike antibodies to gauge overall immunity, encompassing both infections and vaccinations.

Collaborative Endeavour: The research was a conglomerate effort, involving institutions such as St. Michael’s Hospital, Alberta Precision Laboratories, Canadian Blood Services, and the University of Ottawa.

Reference: “The Evolution of SARS-CoV-2 Seroprevalence in Canada – A Time-Series Study, 2020-2023”. CMAJ 2023 August 14.

About the COVID-19 Immunity Task Force: Launched in April 2020, the CITF champions research on SARS-CoV-2 immunity, aiming to assist decision-making on multiple administrative levels. Through collaborations with a broad spectrum of stakeholders, the CITF has backed 120 pivotal studies nationwide, providing invaluable insights into the immunity terrain post-infection and post-vaccination.

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