This is a summary, written by members of the CITF Secretariat, of:

Atkinson A, Albert A, McClymont E, Andrade J, Beach L, Bolotin S, Boucoiran I, Bullard J, Charlton C, Crane J, Dougan S, Forest JC, German GJ, Giguère Y, Girouard G, Hankins C, Krajden M, Lang A, Levett P, Minion J, Neudorf C, Poliquin V, Robinson JL, Scott H, Stein DR, Tran V, Zahariadis G, Zhou HY, Money D; Antenatal Serostudies Team. Canadian SARS-CoV-2 serological survey using antenatal serum samples: a retrospective seroprevalence study. CMAJ Open. 2023 Apr 4;11(2):E305-E313. doi: https://doi.org/10.9778/cmajo.20220045.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in the CMAJ Open, found that seroprevalence data is a very useful mechanism to obtain accurate measures of the prevalence of SARS-CoV-2 infection in the population, and when compared to PCR testing which under detects the number of infections was more reflective of the true burden. The paper shows that seroprevalence in pregnant people was 1.84 to 8.90 times higher than the number of cases recorded by PCR testing among females aged 20–49 years between November and December 2020. This study was led by Dr. Deborah Money (University of British Columbia), in collaboration with CITF-funded or affiliated experts Drs. Shelly Bolotin (University of Toronto), Mel Krajden (UBC), and Catherine Hankins (McGill University).

The authors highlighted that despite varying provincial PCR testing protocols, the findings of higher seroprevalence when compared with PCR test results in nearly all provinces show an important level of undetected SARS-CoV-2 spread in the community. Public health monitoring by serology is, therefore, more accurate and has the advantage of being less costly than PCR testing.

Key findings:

  • The authors found that SARS-CoV-2 antibodies were present in antenatal serum as early as February 2020, indicating SARS-CoV-2 spread in the community early in the pandemic.
  • Before public access to SARS-CoV-2 vaccines in December 2020, overall seropositivity in pregnant people was low across provinces, ranging from 0.33% to 5.38%.
  • In British Columbia, seroprevalence among pregnant people during the Omicron period increased from 4.3% to 43% from November 2021 to June 2022.

This study used existing serological prenatal samples from 10 provinces (British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, Newfoundland and Labrador, Nova Scotia, New Brunswick and Prince Edward Island). Samples were obtained over multiple time periods during the pandemic, from February 2020 to June 2022. PCR-positive pregnant cases per province were obtained from the Canadian Surveillance of COVID-19 in Pregnancy: Epidemiology, Maternal and Infant Outcomes (CANCOVID-Preg) project, and the number of cumulative PCR-positive cases for SARS-CoV-2 infection for females aged 20–49 years by region were obtained from Statistics Canada.