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Canadian SARS-CoV-2 serological survey using antenatal serum samples: a retrospective seroprevalence study
Andrea Atkinson1, Arianne Albert1, Elisabeth McClymont1
1Department of Obstetrics & Gynecology (Atkinson, McClymont, Money), University of British Columbia; Women's Health Research Institute (Albert, Andrade, Money); Department of Pediatrics (McClymont), University of British Columbia, Vancouver, BC; Department of Pathology (Beach), Dalhousie University, Halifax, NS; Dalla Lana School of Public Health (Bolotin), University of Toronto; Public Health Ontario (Bolotin, Tran), Toronto, Ont.; Department of Obstetrics & Gynecology and School of Public Health (Boucoiran), Université de Montréal, Montreal, Que.; Department of Medical Microbiology and Infectious Diseases (Bullard, Stein), University of Manitoba, Winnipeg, Man.; Department of Laboratory Medicine & Pathology (Charlton, H.Y. Zhou), University of Alberta; Public Health Laboratory (ProvLab), Alberta Precision Laboratories (Charlton, R. Zhuo), Edmonton, Alta.; Department of Obstetrics & Gynecology (Crane), Memorial University of Newfoundland, St. John's, NL; Department of Medical Microbiology and Infectious Diseases (Desnoyers, Girouard), Dr. Georges-L.-Dumont University Hospital Centre, Moncton, NB; Better Outcomes Network & Registry Ontario (Dougan), Ont.; CHU de Québec-Université Laval Research Center and Departement of Molecular Biology, Medical Biochemistry, and Pathology (Forest, Giguère), Université Laval, Quebec City, Que.; Health PEI (German, Robinson), Charlottetown, PEI; Department of Laboratory Medicine & Pathobiology (German, Tran), University of Toronto, Toronto, Ont.; Department of Epidemiology, Biostatistics, and Occupational Health (Hankins), McGill University, Montreal, Que.; Department of Pathology & Laboratory Medicine (Krajden, Levett), University of British Columbia, Vancouver, BC; Department of Pathology & Laboratory Medicine (Lang, Minion) and Department of Community Health & Epidemiology (Neudorf), University of Saskatchewan, Saskatoon, Sask.; Department of Obstetrics, Gynecology & Reproductive Sciences (Poliquin), University of Manitoba, Winnipeg, Man.; Department of Obstetrics & Gynecology (Scott), Dalhousie University, Halifax, NS; Cadham Provincial Laboratory (Stein), Manitoba Health, Winnipeg, Man.; Department of Laboratory Medicine (Zahariadis), Memorial University of Newfoundland, St. John's, NL.
Background:
Insufficient data on the rate and distribution of SARS-CoV-2 infection in Canada has presented a substantial challenge to the public health response to the COVID-19 pandemic. Our objective was to assess SARS-CoV-2 seroprevalence in a representative sample of pregnant people throughout Canada, across multiple time points over 2 years of the pandemic, to describe the seroprevalence and show the ability of this process to provide prevalence estimates.
Methods:
This Canadian retrospective serological surveillance study used existing serological prenatal samples across 10 provinces over multiple time periods: Feb. 3-21, 2020; Aug. 24-Sept. 11, 2020; Nov. 16-Dec. 4, 2020; Nov. 15-Dec. 3, 2021; and results from the province of British Columbia during a period in which the SARS-CoV-2 B.1.1.529 (Omicron) variant was predominant, from Nov. 15, 2021, to June 11, 2022. Age and postal code administrative data allowed for comparison with concurrent polymerase chain reactivity (PCR)-positive results collected by Statistics Canada and the Canadian Surveillance of COVID-19 in Pregnancy (CANCOVID-Preg) project.
Results:
Seropositivity in antenatal serum as early as February 2020 indicates SARS-CoV-2 transmission before the World Health Organization's declaration of the pandemic. Seroprevalence in our sample of pregnant people was 1.84 to 8.90 times higher than the recorded concurrent PCR-positive prevalence recorded among females aged 20-49 years in November-December 2020. Overall seropositivity in our sample of pregnant people was low at the end of 2020, increasing to 15% in 1 province by the end of 2021. Seroprevalence among pregnant people in BC during the Omicron period increased from 5.8% to 43% from November 2021 to June 2022.
Interpretation:
These results indicate widespread vulnerability to SARS-CoV-2 infection before vaccine availability in Canada. During the time periods sampled, public health tracking systems were under-reporting infections, and seroprevalence results during the Omicron period indicate extensive community spread of SARS-CoV-2 infection.
