This is a summary, written by members of the CITF Secretariat, of

O’Brien SF, Caffrey N, Yi Q-L, Pambrun C, Drews SJ. SARS-CoV-2 Seroprevalence among Canadian Blood Donors: The Advance of Omicron. Viruses. 2022; 14(11):2336. doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

According to Canadian Blood Services data published in Viruses, infection-related seroprevalence increased with the emergence of the Omicron SARS-CoV-2 variant from September 2021 to June 2022. In collaboration with the CITF, Canadian Blood Services have been monitoring SARS-CoV-2 seroprevalence in Canada since May 2020 by testing blood provided by donors.

Key findings:

  • Infection-induced (anti-nucleocapsid or anti-N) seroprevalence was 4.4% in September 2021 and rose to 50.7% in June 2022. Nearly all the donors were positive for anti-spike protein (anti-S) antibodies (indicative of vaccination) throughout this period.
  • Infection-induced seroprevalence was associated with those who were younger, male, and experienced greater material deprivation, but less social deprivation.
  • The highest rates of infection-induced seropositivity (anti-N) were in Alberta, Saskatchewan, and Manitoba.
  • The anti-S concentration increased between September 2021 to June 2022 and the concentrations were much higher in donors who were anti-N positive.

Despite pre-existing high vaccination rates, there was a substantial increase in infection-induced seroprevalence during the Omicron wave, leading to many more individuals with hybrid immunity.

Canadian Blood Services monitored seroprevalence of SARS-CoV-2 anti-N and anti-S antibodies in blood donors across Canada in 351,414 randomly selected samples between September 2021 to June 2022.  Donors were from nine provinces (excluding Quebec and the Territories) and were screened to ensure they were in good health and not at risk for blood transmissible infections. The proportions of donors were similar to the general population for age, sex, and region, but lower for racialization.