Background. Serological testing was a key component of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) surveillance. Social distancing interventions, resource limitations, and the need for timely data led to serosurveillance studies using a range of recruitment strategies, which likely influenced study representativeness. Characterizing representativeness in surveillance is crucial to identify gaps in sampling coverage and to assess health inequities. Methods. We retrospectively analyzed three pre-existing longitudinal cohorts, two convenience samples using residual blood, and one de novo probabilistic survey conducted in Canada between April 2020 – November 2023. We calculated study specimen counts by age, sex, urbanicity, race/ethnicity, and neighborhood deprivation quintiles. We derived a ′representation ratio′ as a simple metric to assess generalizability to a target population and various sociodemographic strata. Results. The six studies included 1,321,675 specimens. When stratifying by age group and sex, 65% of racialized minority subgroups were moderately underrepresented (representation ratio < 0.75). Representation was generally higher for older Canadians, urban neighborhoods, and neighborhoods with low material deprivation. Rural representation was highest in a study that used outpatient laboratory blood specimens. Racialized minority representation was highest in a de novo probabilistic survey cohort. Conclusion. While no study had adequate representation of all subgroups, less traditional recruitment strategies were more representative of some population dimensions. Understanding demographic representativeness and barriers to recruitment are important considerations when designing population health surveillance studies.

The authors have declared no competing interest.

WAR was supported by funding from Canadian Blood Services and the COVID-19 Immunity Task Force.

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The Faculty of Medicine and Health Sciences Research Ethics Board of McGill University gave ethical approval for this work (study number 22-03-077)

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The authors are not authorized to share individual-level data from any study. Processes are available for researchers to request access to datasets for studies that have undergone institutional ethical approval. Data from Canadian Blood Services and Alberta Precision Laboratories may be made available upon request, subject to internal review, privacy legislation, data sharing agreements, and research ethics approval. The CCAHS-1 study by Statistics Canada can be analyzed for approved projects at Research Data Centres located across Canada (https://www.statcan.gc.ca/en/microdata/data-centres/access). Data are available from the Canadian Longitudinal Study on Aging (www.clsa-elcv.ca) for researchers who meet the criteria for access to de-identified CLSA data. Access to the Ab-C study data can be requested through the COVID-19 Immunity Task Force Databank (https://portal.citf.mcgill.ca/). Access to the CanPath data can be requested through the CanPath data portal (https://portal.canpath.ca/). Analytical code will be available in a public repository upon publication.