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.

September 2021 Results | Antibody wane being observed but breakthrough infections rare

97% of blood donors sampled in September had evidence of antibodies against SARS-CoV-2 acquired through immunization with at least one vaccine dose and/or a past infection. This number was largely driven by vaccination as infection-acquired seroprevalence remained low, at 4.4%, despite the ongoing fourth wave. September results showed evidence of antibody wane in older adults supporting the need for boosters, but breakthrough infections in individuals who received at least one dose of vaccine were infrequent.

Read our detailed September 2021 summary

Previous summaries and reports

August 2020
April 2020 to January 2021

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

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…

Vaccination or infection
(ELISA test developed by Héma-Québec)
Infection only
(ELISA test developed by Héma-Québec)

Data notes:

  • See detailed table of breakdown by Canadian province (excluding Quebec) here
  • Consult the two Héma-Québec reports for the province of Quebec
  • 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 studies tested samples obtained between May 25 to July 9, 2020 and between January 25 to March 11, 2021.

Seroprevalence by racial group over time

Racialized blood donors have been at higher risk of COVID-19 infection throughout the pandemic. Indeed in September 2021, antibodies due to previous SARS-CoV-2 infection were on average 2-times higher among racialized donors (7.6%) compared to self-declared white donors (3.7%) across all geographic areas sampled, similar to previous observations. However, when looking at overall seroprevalence, due to infection or vaccination, rates among sociocultural groups were similar in donors identifying as white (97.0%) and those from racialized groups (98.0%) (including Indigenous, Asian, and other People of Colour).

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 race and source of antibodies for Quebec
January 25 to March 11, 2021

Antibodies induced by…

Infection only
(ELISA test developed by Héma-Québec)
Vaccination or infection
(ELISA test developed by Héma-Québec)

Data notes:

  • 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 questionnaire asked blood donors to state whether they self-identified as Caucasian or non-Caucasian. We took the liberty of changing the language to “racialized” and “white”.
  • The Héma-Québec seroprevalence studies tested samples obtained between January 25 to March 11, 2021.

Seroprevalence by socioeconomic status over time

Antibodies to SARS-CoV-2 (from vaccines or infection) were more prevalent among blood donors residing in higher-income neighbourhoods1 (97.6%) than lower-income neighbourhoods (94.7%), as was the case in previous reports. The most deprived, however, continued to have more antibodies from previous infection than did the least deprived, as was the case in previous reports.

Canada (excluding Quebec and the Territories)

SARS-CoV-2 antibodies

Infection (Roche assay) Vaccine only (Roche assay)

Quebec

Antibodies induced by…

Infection only
(ELISA test developed by Héma-Québec)
Vaccination or infection
(ELISA test developed by Héma-Québec)

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.