96% of Canadian blood donors have evidence of SARS-CoV-2 antibodies, primarily due to vaccination, a rate that has increased from 91% in June and 95% in July. This according to Canadian Blood Services’ 13th seroprevalence report, covering data from August 2021. Nonetheless, targeted efforts to alleviate infection burden and promote vaccine uptake are still required amongst racialized donors and those living in lower-income neighbourhoods, whom, over time, have consistently experienced disproportionately higher levels of infection-acquired antibodies and lower levels of vaccine-induced antibodies.
The latest Canadian Blood Services report included 9,109 people who donated blood between August 15 and 26, 2021, in all Canadian provinces, excluding Quebec.
- In August 2021, antibodies to SARS-CoV-2 among blood donors:
- rose to 96.1%, up from 94.7% in July and 90.8% in June, largely due to vaccination;
- were more prevalent in blood donors residing in higher-income neighbourhoods (98.3%) than lower-income neighbourhoods (93.4%): a significant widening of this gap since July (92.9% in lower-income and 96.7% in higher-income neighbourhoods).
- In August 2021, antibodies due to SARS-CoV-2 infection among blood donors:
- increased to 4.4% from 4.1% in July, comparable to the scenario in June (4.5%);
- were on average 3X higher in racialized donors compared to self-declared white donors across all geographic areas sampled, which marks an increase compared to previous reports;
- were 2X more prevalent in donors from lower-income vs. higher-income neighbourhoods, an expanding gap compared to July;
- were highest amongst blood donors aged 17-24 at 8.4%, in line with previous reports.
Canadian Blood Services registers highest overall seroprevalence yet
The primary source for SARS-CoV-2 antibodies among Canadians is vaccination. Blood donor data in August shows that the median concentration of antibodies against the spike protein of SARS-CoV-2 continues to increase substantially, further confirming widespread vaccine-driven immunity.
While seroprevalence did not differ between socioeconomic groups in July, disparities have returned in the August report. To that end, blood donors living in higher-income neighbourhoods1 are more likely to have SARS-CoV-2 antibodies primarily due to vaccination (98.3%) than those living in more materially deprived neighbourhoods (93.4%).
Early fourth wave magnified in youth, racialized groups, and poorer neighbourhoods
Levels of seroprevalence due to a past SARS-CoV-2 infection remained low in August 2021, at 4.4%.
- Infection-acquired seroprevalence had risen gradually since April (3.2% in April, 4.0% in May, 4.5% in June), dipping slightly in July (4.1%).
- Seroprevalence due to a past infection consistently remains highest in the youngest age bracket (17-to-24-years-old: 8.4% in August)
- Similar to what was seen in the third wave, the fourth wave, which began in August 2021, is concentrated in racialized groups (11.1%) and donors from less affluent neighbourhoods (7.9%), compared to white donors (3.3%) and donors from more affluent neighbourhoods (3.3%), respectively.
Repeat testing of frequent donors: a sub-study
Among nearly 17,800 donors who donated blood more than once since January 2021, the majority antibody test profile (seen in 53.0% of donors) was unvaccinated at the time of their first donation2 and vaccinated by their most recent donation3. Additionally, eleven donors who were vaccinated based on a positive test for only anti-spike antibodies, later tested positive for both spike and nucleocapsid protein antibodies, suggesting potential breakthrough SARS-CoV-2 infection.
Explore our interactive webpage featuring the latest aggregated data gathered by Canadian Blood Services and Héma-Québec on SARS-CoV-2 seroprevalence in Canada.
1 Measured using the Material Deprivation Index based on postal codes.
2 Tested negative for SARS-CoV-2 spike and nucleocapsid, two of the proteins used to measure the presence of COVID-19-specific antibodies.
3 Tested positive for SARS-CoV-2 spike and negative for nucleocapsid, learn more about this here.