Infection-acquired seroprevalence increased in July: Canadian Blood Services

Due to continued transmission of the newer Omicron variants (BA.4 and BA.5) in Canada, infection-acquired seropositivity increased within the blood donor community, from 50.7% at the end of June to 54% by the end of July, with a modest week-to-week change throughout July. Donors aged 17- to 24-years-old had the highest infection-acquired seroprevalence rate of any age group, at 71.2%. The increase in the concentration of vaccine-induced antibodies in those over 60 observed in May and June – most likely driven by the uptake of fourth vaccine doses – levelled off in July. Almost all blood donors were still positive for vaccine-induced antibodies.

Key findings:

• Consistent with previous surveys, donors aged 17- to 24-years-old had the highest infection-acquired (anti-N) seroprevalence rate (71.2%) of all age groups. However, the infection-acquired seroprevalence rate increased in all age groups compared to June.

• There was a modest week-to-week increase in infection-acquired seropositivity throughout July: from 52.3% to 52.7% to 54.7% to 56.5%.

• Seroprevalence rates increased in July compared to June in all provinces except PEI (although the sample sizes are small). However, the increase was only statistically significant in British Columbia, Ontario, New Brunswick, and Newfoundland, despite smaller sample sizes in the latter two.
• This latest data emphasize the persistent inequities in infection burden among racialized communities, which continued to have higher seroprevalence than self-declared white donors (62.3% vs. 52%).
• The data show people with the most social contact had a greater chance of having infection-acquired antibodies (55.6%), versus those with the least social contact (51%) in July. June percentages were 51.5% and 48%, respectively.
• The current data also highlight the most materially deprived still had a higher infection burden (57.9%) in July, compared to the least materially deprived (53.3%). The June percentages were 51.1% vs. 47.9%, respectively.
• Almost all blood donors (100%) tested positive for anti-S antibodies, predominantly driven by vaccinations.

• The increase in the median spike concentrations (due to vaccination) observed in May and June, thanks to the uptake of fourth vaccine doses, levelled off in July, especially among those over the age of 60.

The latest report builds on the June 2022 report and includes samples from 31,275 people over the age of 17 who donated blood between July 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.