Infection-acquired seroprevalence increased again in August: Canadian Blood Services

Omicron and its subvariants (BA.4 and BA.5) continued to spread in Canada in August. By the last week of August, 60% of blood donors had infection-acquired seropositivity, up from 56.5% at the end of July. Younger age groups continued to be the most affected, with over 75% of 17- to 24-year-olds showing they had had a previous SARS-CoV-2 infection. Almost all blood donors were found to be positive for anti-S antibodies, predominantly driven by vaccination.

Key findings:

• There was a modest week-to-week increase in infection-acquired seropositivity throughout August: from 56.8% to 58.3% to 58.6% to 60%.
• Consistent with previous surveys, donors aged 17- to 24-years old continued to have the highest infection-acquired (anti-N) seroprevalence rate – 75.1%. This was compared to 67.6% for those 25-39 years, 60.5% for those aged 40-59 years, and 41.1% for those 60+ years. The increase in the rate of seroprevalence was statistically significant for all age groups.
• Seroprevalence rates due to infection increased in August compared to July in all provinces. The increase was statistically significant for all provinces except for Saskatchewan and Prince Edward Island.
• Racialized blood donors continued to have higher infection-acquired seroprevalence than self-declared white donors (71% vs 56.6%).
• The data highlight that the difference in the infection rates in people who had the most social contact in comparison to those who had the least social contact showed a slight increase in August (61% vs 57%) when compared to July (55.6% vs 51%).
• Canadian Blood Service data continued to highlight the disparity in the burden of infection between the most materially deprived and the least materially deprived population groups. Among the most deprived, the infection rate rose to 62% (up from 57.9% in July). Among the least deprived, there was a more modest increase, to 57% in August, from 53.3% in July.
• Almost all blood donors (100%) tested positive for anti-S antibodies, predominantly driven by vaccinations.

Conclusion

Vaccine-induced (anti-S) antibodies were present among almost all blood donors in August in all the age groups including participants above 60.

The latest report builds on the July 2022 report and includes samples from 35,121  people over the age of 17 who donated blood between August 1^st and 31^st, 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.