TY - JOUR T1 - Canadian SARS-CoV-2 serological survey using antenatal serum samples: a retrospective seroprevalence study JF - CMAJ Open JO - CMAJ SP - E305 LP - E313 DO - 10.9778/cmajo.20220045 VL - 11 IS - 2 AU - Andrea Atkinson AU - Arianne Albert AU - Elisabeth McClymont AU - Janice Andrade AU - Lori Beach AU - Shelly Bolotin AU - Isabelle Boucoiran AU - Jared Bullard AU - Carmen Charlton AU - Joan Crane AU - Shelley Dougan AU - Jean-Claude Forest AU - Greg J. German AU - Yves Giguère AU - Gabriel Girouard AU - Catherine Hankins AU - Mel Krajden AU - Amanda Lang AU - Paul Levett AU - Jessica Minion AU - Cory Neudorf AU - Vanessa Poliquin AU - Jason L. Robinson AU - Heather Scott AU - Derek R. Stein AU - Vanessa Tran AU - George Zahariadis AU - Hong Y. Zhou AU - Deborah Money AU - The Antenatal Serostudies Team Y1 - 2023/03/01 UR - http://www.cmajopen.ca/content/11/2/E305.abstract N2 - 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. ER -