@article {AtkinsonE305, author = {Andrea Atkinson and Arianne Albert and Elisabeth McClymont and Janice Andrade and Lori Beach and Shelly Bolotin and Isabelle Boucoiran and Jared Bullard and Carmen Charlton and Joan Crane and Shelley Dougan and Jean-Claude Forest and Greg J. German and Yves Gigu{\`e}re and Gabriel Girouard and Catherine Hankins and Mel Krajden and Amanda Lang and Paul Levett and Jessica Minion and Cory Neudorf and Vanessa Poliquin and Jason L. Robinson and Heather Scott and Derek R. Stein and Vanessa Tran and George Zahariadis and Hong Y. Zhou and Deborah Money and The Antenatal Serostudies Team}, title = {Canadian SARS-CoV-2 serological survey using antenatal serum samples: a retrospective seroprevalence study}, volume = {11}, number = {2}, pages = {E305--E313}, year = {2023}, doi = {10.9778/cmajo.20220045}, publisher = {Canadian Medical Association Open Access Journal}, abstract = {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{\textendash}21, 2020; Aug. 24{\textendash}Sept. 11, 2020; Nov. 16{\textendash}Dec. 4, 2020; Nov. 15{\textendash}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){\textendash}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{\textquoteright}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{\textendash}49 years in November{\textendash}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.}, URL = {https://www.cmajopen.ca/content/11/2/E305}, eprint = {https://www.cmajopen.ca/content/11/2/E305.full.pdf}, journal = {Canadian Medical Association Open Access Journal} }