Canadian Blood Services & Héma-Québec:
Reporting Canadian Seroprevalence Over Time

The COVID-19 Immunity Task Force (CITF) has been partnering with Canadian Blood Services and Héma-Québec since Spring 2020 to track the presence of antibodies in the Canadian population. The CITF funds the Canadian Blood Services monthly surveys across nine provinces and has supported Héma-Québec to undertake analyses that make their periodic seroprevalence surveys (funded by Quebec’s Health and Social Services Ministry) comparable with the Canadian Blood Services surveys.

March 2022 results | 30% of Canadian Blood Services donors infected with SARS-CoV-2 by end of March 2022

Consistent with the ongoing transmission of the Omicron variant, infection-acquired seropositivity increased gradually throughout March, from 27% to 30%. The newest data from Canadian Blood Services emphasize the persisting inequities in infection burden among young adults, racialized communities, and those residing in lower-income neighbourhoods. In their latest report, they also estimate that 30% of unvaccinated blood donors had evidence of a recent infection with the virus. This, compared to about 18% of vaccinated donors.

The state of infection-induced seroprevalence in Canada

The interactive map below was produced by the CITF modeling team based on Canadian Blood Services data. Based on data from blood donors, this map illustrates the percentage of Canadian adults with infection-acquired antibodies by the end of March (data from Quebec is until mid-March).

Data Note: Canada Blood Services and Hema-Quebec use different laboratory methods to test for Spike and Nucleocapsid antibodies. Results for Quebec are, therefore, not directly comparable to those from other provinces.

SARS-CoV-2 antibody seroprevalence in
Canadian blood donors over time

Canada (excluding Quebec and the Territories)

Antibodies induced by…

Infection or vaccination (Roche assay) Vaccine only (Roche assay)
Infection (Roche assay) Infection (Abbott assay)

Data notes:

  • Click here for details on the dates when blood samples were taken and the mid-point used for CITF plotting.
  • Roche N assay results are proxy for previous infection with SARS-CoV-2, Roche S results are proxy for humoral immunity by either infection or vaccination, and Roche S-only results are proxy for vaccine-induced immunity. This is because vaccines produce antibodies to the spike (S) protein (reactive to Roche S) but not the nucleocapsid (N) protein (reactive to Roche N); whereas infection will usually produce antibodies captured by both Roche S and N.
  • Want more details? See detailed data table.

Seroprevalence by province over time

Compared to February, infection-acquired seropositivity increased in all provinces covered by Canadian Blood Services (CBS data excludes Quebec), except for Prince Edward Island and Newfoundland and Labrador. Data from Quebec represents samples taken through to mid-March 2022, whereas data from the other provinces reflects samples taken until end of March 2022.

Data Note: Canada Blood Services and Hema-Quebec use different laboratory methods to test for Spike and Nucleocapsid antibodies. Results for Quebec are, therefore, not directly comparable to those from other provinces.

British Columbia

Alberta

Saskatchewan

Manitoba

Ontario

New Brunswick

Nova Scotia

Prince Edward Island

Newfoundland

Antibodies induced by…

Infection or vaccination (Roche assay) Vaccine only (Roche assay)
Infection (Roche assay) Infection (Abbott assay)

Quebec

Antibodies induced by:

Infection only (ELISA test ratio approach developed by Héma-Québec)

 

Data Note: Canada Blood Services and Hema-Quebec use different laboratory methods to test for Spike and Nucleocapsid antibodies. Results for Quebec are, therefore, not directly comparable to those from other provinces.

Infection-acquired seroprevalence over time in Canada: a detailed interactive graph

This graph amalgamates Canadian Blood Services data since the beginning of the pandemic. It allows you to view the rates of infection-acquired seropositivity according to material deprivation, racial group, and age, providing insight about the characteristics of who has been most adversely affected by COVID-19. Such data can assist officials and policy makers when they are deploying resources and can help address issues regarding access to public health, disseminating information, and ensuring equity for all Canadians.

Please click on the red buttons at the top, “material deprivation”, “racial group”, or “age” to filter the results. You can also double click on the legend to isolate a trace.

Seroprevalence by age

Canada (excluding Quebec and the Territories)

While infection-acquired seropositivity increased across all age groups, blood donors in the 17-24-year-old bracket, who have consistently been the most impacted, exhibited a seropositivity rate of 44.3%, up from 36.3% in February.

Quebec

The proportion of donors with infection-acquired antibodies decreased according to age, from younger to older adults: 40.3% of donors 18 to 24 years old, 38.1% of donors aged 25-39 years old, 27.9% of donors aged 40-59 years old, and 18.7% of donors aged 60 and older (data for mid-March). Donors aged 60 and older experienced the largest increase in infection-acquired seropositivity over time across all age categories; a 6.6 time increase from 2.8% in January to 18.7% by mid-March.

Data Note: Canada Blood Services and Hema-Quebec use different laboratory methods to test for Spike and Nucleocapsid antibodies. Results for Quebec are, therefore, not directly comparable to those from other provinces.

Seroprevalence by racial group over time

As has consistently been the case throughout the pandemic, donors belonging to a racialized group were more likely to have infection-acquired antibodies (38.6%) than donors who identified as white (26.3%).

Seroprevalence by race, month, and source of antibodies for Canada (excluding Quebec and the Territories)

SARS-CoV-2 antibodies

Infection (Roche assay) Vaccine only (Roche assay)

Data notes:

  • The bar height shows the estimated proportion of the subgroup who had antibodies to SARS-CoV-2, adjusted for assay sensitivity and specificity and standardized to the Canadian population. Error bars show 95% confidence intervals.
  • Antibodies from vaccine only are in red = anti-S IgG positive and anti-N IgG negative.
  • Antibodies from infection are in blue = positive for anti-nucleocapsid IgG, with anti-spike possibly boosted by vaccine.

Seroprevalence by socioeconomic status over time

Canada (excluding Quebec and the Territories)

Rates of infection-acquired seropositivity were greater among donors from lower income compared to higher income neighbourhoods1 (36.6% vs. 25.9%, respectively). This indicates a widening of the gap between socioeconomic groups, as the February report showed seropositivity was 22.4% in more affluent neighbourhoods as compared with 28.9% in more deprived neighbourhoods.

1 As measured by the Material Deprivation Index, which makes use of postal code data.

SARS-CoV-2 antibodies

Infection (Roche assay) Vaccine only (Roche assay)

Data notes:

  • The Material Deprivation index is an indicator for the deprivation of goods and services in a given community. It is developed using postal codes and data from the Canadian Census on household income, unemployment rate, and high school education rate.
  • Quebec data gathered and analyzed by Héma-Québec used an ELISA assay developed by Héma-Québec and not Abbott or Roche, as in the Canadian Blood Services serosurveys. The Héma-Québec assay detects antibodies from either infection or vaccination (detects antibodies against the Receptor Binding Domain (RBD) of SARS-CoV-2).
  • Vaccination against SARS-CoV-2 began in December 2020 in Quebec. For each donor included in the study, Héma-Québec obtained their vaccination status, including their vaccination dates and the type of vaccine product, from the provincial vaccination registry named SI-PMI, managed by Quebec’s Health and Social Services Ministry.
  • The Héma-Québec seroprevalence study tested samples obtained between January 25 to March 11, 2021.

Quebec

The proportion of donors with infection-acquired antibodies decreased according to age, from younger to older adults: 40.3% of donors 18 to 24 years old, 38.1% of donors aged 25-39 years old, 27.9% of donors aged 40-59 years old, and 18.7% of donors aged 60 and older (data for mid-March). Donors aged 60 and older experienced the largest increase in infection-acquired seropositivity over time across all age categories; a 6.6 time increase from 2.8% in January to 18.7% by mid-March.

Data Note: Canada Blood Services and Hema-Quebec use different laboratory methods to test for Spike and Nucleocapsid antibodies. Results for Quebec are, therefore, not directly comparable to those from other provinces.

Previous reports

February 2022
January 2022
December 2021

Previous summaries

Mid-February 2022
Mid-January 2022
December 2021
November 2021
October 2021
September 2021
August 2021
July 2021
June 2021
May 2021
January 2021
Oct/Nov 2020
May/June 2020