This is a summary written by members of the CITF Secretariat of Canadian Blood Services’ mid-March 2023 report of data gathered from blood donations. The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.
Despite all donors having vaccine-induced antibodies, the latest CITF-funded seroprevalence report from Canadian Blood Services showed overall seroprevalence due to infection was 78.3% by mid-March, consistent with the continued presence of circulating Omicron subvariants. This estimate was similar to the 77.6% estimate recorded in February 2023. Among the youngest donors (aged 17-24), almost 90% had antibodies due to infection by mid-March.
- There was no statistically relevant change over the 15-day reporting period from 77.5% in the last week of February to 78.0% in the first week of March and 78.3% in the second week of March.
- Compared to other age groups, donors aged 17-24 in the week of March 8-15 had the highest infection-acquired seroprevalence at 89.4%. Those aged 60+ had the lowest seroprevalence due to infection at 66.6%.
- Self-declared racialized groups continued to have higher seroprevalence compared with white donors (83.7% vs 76.7%) in the week of March 8-15. In that same week, self-declared Indigenous donors had an infection-acquired seroprevalence of 78.5%, while for self-declared Asians it was 83.8%.
- The difference in infection-acquired seroprevalence observed between the most and the least materially deprived populations was 3.5% in the week of March 8-15: seroprevalence was 81.1% among the most deprived and 77.6% among the least deprived donors.
- Anti-spike antibodies were present in all blood donors. Since IgG anti-spike antibodies arise after SARS-CoV-2 infection as well as vaccination, this high prevalence reflects both vaccination and infections. However, since January 2023, anti-spike antibodies have started to decline, particularly in older age groups.
The latest report builds on the mid-March 2023 report and includes samples from 15,209 unique donors over the age of 17 who donated blood between March 1st and March 15th, 2023 across 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.