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

Canadian Blood Services’ May 2022 report to the CITF

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

Consistent with the ongoing transmission of the Omicron variant, infection-acquired seropositivity increased in the blood donor community gradually throughout May, from 36.71% at the end of April to 48.96% at the end of May, according to data from Canadian Blood Services. Concentrations of antibodies due to vaccination (anti-spike (S) antibodies) were high by September 2021 but gradually decreased over the following few months (expected, as immunity wanes over time). Those vaccine-induced antibody concentrations did increase in all age groups again by February 2022, likely due to the administration of third vaccine doses. In the 60+ age group, anti-S antibodies rose in May, consistent with the administration of fourth doses to older Canadians.

Key findings:

  • Among repeat tested donors, new infections in unvaccinated donors increased from June 2021 (1.53%) to 9.12% in January 2022 and 46.83% in May 2022.
  • Potential breakthrough infections have increased dramatically over the first five months of 2022, from 5.19% in January to 31.02% in May.
  • Consistent with previous surveys, donors aged 17-24 years old had the highest infection-acquired (anti-nucleocapsid (N)) seroprevalence rate compared to other age groups (64.47%). However, the seroprevalence rate increased in all age groups compared to April.
  • Infection-acquired seroprevalence increased in all provinces in May compared to April, with the exception of Prince Edward Island. However, few samples were tested in the Atlantic provinces.
  • The data also emphasize persistent inequalities in infection burden based on socioeconomic status. Individuals from low socioeconomic groups (most deprived – Q5) continued to have higher infection-acquired seroprevalence when compared to the high socioeconomic individuals (least deprived – Q1) (47.8% vs 41.95%).
  • This latest CBS data emphasize the persisting inequities in infection burden within racialized communities. Racialized donors continued to have higher infection-acquired seroprevalence compared with white donors (54.35% vs 44.31%).
  • Nearly all blood donors (100% CI, 99.79, 100.00) tested positive for anti-S antibodies, most likely induced by vaccination.
  • In May, the median spike concentrations increased, especially among those over the age of 60, likely due to the administration of a fourth dose.


Vaccine-induced antibody concentrations (anti-S) were high among blood donors in May. The data saw concentrations of vaccine-induced antibodies rise in older adults in May due to fourth doses.

The latest report builds on the mid-May report and includes samples from 31, 764 people over the age of 17 who donated blood between May 1 to 31, 2022, in all of Canada excluding Quebec and the Territories.

It should be noted that individuals who choose to donate blood are generally in good health and are more likely to live in populous urban areas. Percentages were adjusted for test characteristics and population distribution.

Explore our interactive webpage updated every month, featuring the latest aggregated data gathered by the Canadian Blood Services and Héma-Québec on SARS-CoV-2 seroprevalence in Canada.