Seropositivity of SARS-CoV-2 in an unvaccinated cohort in British Columbia, Canada: a cross-sectional survey with dried blood spot samples

C Sarai Racey; Amy Booth; Arianne Albert; Laurie W Smith; Mel Krajden; Melanie C M Murray; Hélène C F Côté; Anna Gottschlich; David M Goldfarb; Manish Sadarangani; Liisa A M Galea; Angela Kaida; Lori A Brotto; Gina S Ogilvie

doi:10.1136/bmjopen-2022-062567

Seropositivity of SARS-CoV-2 in an unvaccinated cohort in British Columbia, Canada: a cross-sectional survey with dried blood spot samples

BMJ Open. 2022 Aug 29;12(8):e062567. doi: 10.1136/bmjopen-2022-062567.

Authors

C Sarai Racey^{1

2}, Amy Booth^{1

2}, Arianne Albert², Laurie W Smith^{2

3}, Mel Krajden⁴, Melanie C M Murray^{2

5}, Hélène C F Côté^{2

6}, Anna Gottschlich^{1

2}, David M Goldfarb⁶, Manish Sadarangani^{7

8}, Liisa A M Galea^{2

9}, Angela Kaida^{2

10}, Lori A Brotto^{2

11}, Gina S Ogilvie^{12

2

4}

Affiliations

¹ School of Population and Public Health, The University of British Columbia, Vancouver, British Columbia, Canada.
² British Columbia Women's Hospital and Health Centre, Women's Health Research Institute, Vancouver, British Columbia, Canada.
³ Cancer Control Research, BC Cancer Agency, Vancouver, British Columbia, Canada.
⁴ BC Centre for Disease Control, Vancouver, British Columbia, Canada.
⁵ Faculty of Medicine, The University of British Columbia, Vancouver, British Columbia, Canada.
⁶ Pathology and Laboratory Medicine, The University of British Columbia Faculty of Medicine, Vancouver, British Columbia, Canada.
⁷ Department of Pediatrics, The University of British Columbia, Vancouver, British Columbia, Canada.
⁸ Vaccine Evaluation Center, BC Children's Hospital Research Institute, Vancouver, British Columbia, Canada.
⁹ Department of Psychology, The University of British Columbia, Vancouver, British Columbia, Canada.
¹⁰ Faculty of Health Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
¹¹ Department of Obstetrics & Gynaecology, The University of British Columbia, Vancouver, British Columbia, Canada.
¹² School of Population and Public Health, The University of British Columbia, Vancouver, British Columbia, Canada gina.ogilvie@cw.bc.ca.

Abstract

Objectives: Gathering population-based data on prevalence of SARS-CoV-2 infection is vital to the public health response and planning. Current seroprevalence data in BC are limited with respect to considerations of how socioeconomic and demographic factors, such as age, sex, gender, income, identifying as a visibility minority and occupation, are related to SARS-CoV-2 antibody detection due to infection-acquired immunity. We aimed to estimate the SARS-CoV-2 seropositivity in a cohort of British Columbians, using at-home self-collected dried blood spot (DBS) samples.

Design: This cross-sectional study included online surveys that collected sociodemographic and COVID-19 vaccine receipt information, and an at-home DBS collection kit.

Setting: British Columbia (BC), Canada.

Participants: Eligible participants were aged 25-69 years and residents of BC.

Primary outcome measure: SARS-CoV-2 anti-spike IgG antibody detection in unvaccinated individuals. Adjusted incidence rate ratios (aIRR) explored factors associated with seropositivity.

Results: SARS-CoV-2 serology was performed on a total of 4048 unvaccinated participants 25-69 years of age who submitted DBS samples taken from November 2020 to June 2021. A total of 118 seropositive cases were identified, for an estimated overall seropositivity of 2.92% (95% CI 2.42% to 3.48%). Participants identifying as a visible minority had a higher seropositivity, 5.1% vs 2.6% (p=0.003), compared with non-visible minority participants. After adjustment by age and sex, identifying as a visible minority (aIRR=1.85, 95% CI 1.20 to 2.84) remained the only significant factor associated with SARS-CoV-2 antibody detection in this cohort of unvaccinated individuals.

Conclusions: SARS-CoV-2 seropositivity in the BC population due to infection-acquired immunity was low. Seropositivity indicated that among those unvaccinated, visible minority communities have been most impacted. Continued monitoring of SARS-CoV-2 serology due to both infection-acquired and vaccine-acquired immunity will be vital in public health planning and pandemic response.

Keywords: COVID-19; EPIDEMIOLOGY; PUBLIC HEALTH; Public health.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adult
Aged
Antibodies, Viral
British Columbia / epidemiology
COVID-19 Vaccines
COVID-19* / epidemiology
Cross-Sectional Studies
Humans
Middle Aged
SARS-CoV-2*
Seroepidemiologic Studies

Substances

Antibodies, Viral
COVID-19 Vaccines