The evolution of SARS-CoV-2 seroprevalence in Canada: a time-series study, 2020-2023

doi:10.1503/cmaj.230249

. 2023 Aug 14;195(31):E1030-E1037.

doi: 10.1503/cmaj.230249.

The evolution of SARS-CoV-2 seroprevalence in Canada: a time-series study, 2020-2023

Tanya J Murphy¹, Hanna Swail¹, Jaspreet Jain¹, Maureen Anderson¹, Philip Awadalla¹, Lesley Behl¹, Patrick E Brown¹, Carmen L Charlton¹, Karen Colwill¹, Steven J Drews¹, Anne-Claude Gingras¹, Deena Hinshaw¹, Prabhat Jha¹, Jamil N Kanji¹, Victoria A Kirsh¹, Amanda L S Lang¹, Marc-André Langlois¹, Stephen Lee¹, Antoine Lewin¹, Sheila F O'Brien¹, Chantale Pambrun¹, Kimberly Skead¹, David A Stephens², Derek R Stein¹, Graham Tipples¹, Paul G Van Caeseele¹, Timothy G Evans¹, Olivia Oxlade¹, Bruce D Mazer¹, David L Buckeridge¹

Affiliations

¹ COVID-19 Immunity Task Force (Murphy, Swail, Jain, Evans, Oxlade, Mazer, Buckeridge), School of Population and Global Health, McGill University, Montréal, Que.; Department of Community Health and Epidemiology (Anderson, Behl), University of Saskatchewan; Saskatchewan Health Authority (Anderson), Population Health, Saskatoon, Sask.; Department of Molecular Genetics (Awadalla), University of Toronto; Department of Computational Biology (Awadalla), Ontario Institute for Cancer Research; Centre for Global Health Research (Brown), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Charlton, Hinshaw, Tipples), Alberta Precision Laboratories, University of Alberta Hospital; Department of Laboratory Medicine and Pathology (Charlton, Tipples), and Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alta.; Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital (Colwill, Gingras), Sinai Health System, Toronto, Ont.; Canadian Blood Services (Drews); Department of Laboratory Medicine and Pathology (O'Brien, Pambrun, Drews), University of Alberta, Edmonton, Alta.; Department of Molecular Genetics (Gingras, Skead), University of Toronto; Centre for Global Health Research (Jha), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Kanji), Alberta Precision Laboratories, Foothills Medical Centre, and Section of Medical Microbiology (Kanji), Department of Pathology and Laboratory Medicine, and Division of Infectious Diseases, Department of Medicine, University of Calgary, Calgary, Alta.; Ontario Health Study (Kirsh, Skead), Ontario Institute for Cancer Research; Department of Molecular Genetics (Kirsh, Skead), and Dalla Lana School of Public Health (Kirsh), University of Toronto, Toronto, Ont.; Roy Romanow Provincial Lab (Lang), Saskatchewan Health Authority; College of Medicine (Lang), University of Saskatchewan, Saskatoon, Sask.; Department of Biochemistry, Microbiology and Immunology (Langlois), and Centre for Infection, Immunity and Inflammation (Langlois), University of Ottawa, Ottawa, Ont.; Division of Infectious Diseases-Regina (Lee), University of Saskatchewan; Saskatchewan Health Authority (Lee), Saskatoon, Sask.; Medical Affair and Innovation (Lewin), Héma-Québec, Montréal, Que.; Departments of Epidemiology and Community Medicine (O'Brien), and Pathology and Laboratory Medicine (Pambrun), Faculty of Medicine, University of Ottawa, Ottawa, Ont.; Department of Mathematics & Statistics (Stephens), McGill University, Montréal, Que.; Department of Medical Microbiology (Stein, Van Caeseele), University of Manitoba, and Cadham Provincial Laboratory, Winnipeg, Man.; School of Population and Global Health (Evans), McGill University; The Research Institute of the McGill University Health Centre (Mazer, Buckeridge), Montréal, Que.
² COVID-19 Immunity Task Force (Murphy, Swail, Jain, Evans, Oxlade, Mazer, Buckeridge), School of Population and Global Health, McGill University, Montréal, Que.; Department of Community Health and Epidemiology (Anderson, Behl), University of Saskatchewan; Saskatchewan Health Authority (Anderson), Population Health, Saskatoon, Sask.; Department of Molecular Genetics (Awadalla), University of Toronto; Department of Computational Biology (Awadalla), Ontario Institute for Cancer Research; Centre for Global Health Research (Brown), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Charlton, Hinshaw, Tipples), Alberta Precision Laboratories, University of Alberta Hospital; Department of Laboratory Medicine and Pathology (Charlton, Tipples), and Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alta.; Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital (Colwill, Gingras), Sinai Health System, Toronto, Ont.; Canadian Blood Services (Drews); Department of Laboratory Medicine and Pathology (O'Brien, Pambrun, Drews), University of Alberta, Edmonton, Alta.; Department of Molecular Genetics (Gingras, Skead), University of Toronto; Centre for Global Health Research (Jha), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Kanji), Alberta Precision Laboratories, Foothills Medical Centre, and Section of Medical Microbiology (Kanji), Department of Pathology and Laboratory Medicine, and Division of Infectious Diseases, Department of Medicine, University of Calgary, Calgary, Alta.; Ontario Health Study (Kirsh, Skead), Ontario Institute for Cancer Research; Department of Molecular Genetics (Kirsh, Skead), and Dalla Lana School of Public Health (Kirsh), University of Toronto, Toronto, Ont.; Roy Romanow Provincial Lab (Lang), Saskatchewan Health Authority; College of Medicine (Lang), University of Saskatchewan, Saskatoon, Sask.; Department of Biochemistry, Microbiology and Immunology (Langlois), and Centre for Infection, Immunity and Inflammation (Langlois), University of Ottawa, Ottawa, Ont.; Division of Infectious Diseases-Regina (Lee), University of Saskatchewan; Saskatchewan Health Authority (Lee), Saskatoon, Sask.; Medical Affair and Innovation (Lewin), Héma-Québec, Montréal, Que.; Departments of Epidemiology and Community Medicine (O'Brien), and Pathology and Laboratory Medicine (Pambrun), Faculty of Medicine, University of Ottawa, Ottawa, Ont.; Department of Mathematics & Statistics (Stephens), McGill University, Montréal, Que.; Department of Medical Microbiology (Stein, Van Caeseele), University of Manitoba, and Cadham Provincial Laboratory, Winnipeg, Man.; School of Population and Global Health (Evans), McGill University; The Research Institute of the McGill University Health Centre (Mazer, Buckeridge), Montréal, Que. david.buckeridge@mcgill.ca bruce.mazer@mcgill.ca.

PMID: 37580072
PMCID: PMC10426348
DOI: 10.1503/cmaj.230249

The evolution of SARS-CoV-2 seroprevalence in Canada: a time-series study, 2020-2023

Tanya J Murphy et al. CMAJ. 2023.

. 2023 Aug 14;195(31):E1030-E1037.

doi: 10.1503/cmaj.230249.

Authors

Affiliations

¹ COVID-19 Immunity Task Force (Murphy, Swail, Jain, Evans, Oxlade, Mazer, Buckeridge), School of Population and Global Health, McGill University, Montréal, Que.; Department of Community Health and Epidemiology (Anderson, Behl), University of Saskatchewan; Saskatchewan Health Authority (Anderson), Population Health, Saskatoon, Sask.; Department of Molecular Genetics (Awadalla), University of Toronto; Department of Computational Biology (Awadalla), Ontario Institute for Cancer Research; Centre for Global Health Research (Brown), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Charlton, Hinshaw, Tipples), Alberta Precision Laboratories, University of Alberta Hospital; Department of Laboratory Medicine and Pathology (Charlton, Tipples), and Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alta.; Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital (Colwill, Gingras), Sinai Health System, Toronto, Ont.; Canadian Blood Services (Drews); Department of Laboratory Medicine and Pathology (O'Brien, Pambrun, Drews), University of Alberta, Edmonton, Alta.; Department of Molecular Genetics (Gingras, Skead), University of Toronto; Centre for Global Health Research (Jha), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Kanji), Alberta Precision Laboratories, Foothills Medical Centre, and Section of Medical Microbiology (Kanji), Department of Pathology and Laboratory Medicine, and Division of Infectious Diseases, Department of Medicine, University of Calgary, Calgary, Alta.; Ontario Health Study (Kirsh, Skead), Ontario Institute for Cancer Research; Department of Molecular Genetics (Kirsh, Skead), and Dalla Lana School of Public Health (Kirsh), University of Toronto, Toronto, Ont.; Roy Romanow Provincial Lab (Lang), Saskatchewan Health Authority; College of Medicine (Lang), University of Saskatchewan, Saskatoon, Sask.; Department of Biochemistry, Microbiology and Immunology (Langlois), and Centre for Infection, Immunity and Inflammation (Langlois), University of Ottawa, Ottawa, Ont.; Division of Infectious Diseases-Regina (Lee), University of Saskatchewan; Saskatchewan Health Authority (Lee), Saskatoon, Sask.; Medical Affair and Innovation (Lewin), Héma-Québec, Montréal, Que.; Departments of Epidemiology and Community Medicine (O'Brien), and Pathology and Laboratory Medicine (Pambrun), Faculty of Medicine, University of Ottawa, Ottawa, Ont.; Department of Mathematics & Statistics (Stephens), McGill University, Montréal, Que.; Department of Medical Microbiology (Stein, Van Caeseele), University of Manitoba, and Cadham Provincial Laboratory, Winnipeg, Man.; School of Population and Global Health (Evans), McGill University; The Research Institute of the McGill University Health Centre (Mazer, Buckeridge), Montréal, Que.
² COVID-19 Immunity Task Force (Murphy, Swail, Jain, Evans, Oxlade, Mazer, Buckeridge), School of Population and Global Health, McGill University, Montréal, Que.; Department of Community Health and Epidemiology (Anderson, Behl), University of Saskatchewan; Saskatchewan Health Authority (Anderson), Population Health, Saskatoon, Sask.; Department of Molecular Genetics (Awadalla), University of Toronto; Department of Computational Biology (Awadalla), Ontario Institute for Cancer Research; Centre for Global Health Research (Brown), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Charlton, Hinshaw, Tipples), Alberta Precision Laboratories, University of Alberta Hospital; Department of Laboratory Medicine and Pathology (Charlton, Tipples), and Li Ka Shing Institute of Virology, University of Alberta, Edmonton, Alta.; Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital (Colwill, Gingras), Sinai Health System, Toronto, Ont.; Canadian Blood Services (Drews); Department of Laboratory Medicine and Pathology (O'Brien, Pambrun, Drews), University of Alberta, Edmonton, Alta.; Department of Molecular Genetics (Gingras, Skead), University of Toronto; Centre for Global Health Research (Jha), Unity Health Toronto and University of Toronto, Toronto, Ont.; Public Health Laboratory (Kanji), Alberta Precision Laboratories, Foothills Medical Centre, and Section of Medical Microbiology (Kanji), Department of Pathology and Laboratory Medicine, and Division of Infectious Diseases, Department of Medicine, University of Calgary, Calgary, Alta.; Ontario Health Study (Kirsh, Skead), Ontario Institute for Cancer Research; Department of Molecular Genetics (Kirsh, Skead), and Dalla Lana School of Public Health (Kirsh), University of Toronto, Toronto, Ont.; Roy Romanow Provincial Lab (Lang), Saskatchewan Health Authority; College of Medicine (Lang), University of Saskatchewan, Saskatoon, Sask.; Department of Biochemistry, Microbiology and Immunology (Langlois), and Centre for Infection, Immunity and Inflammation (Langlois), University of Ottawa, Ottawa, Ont.; Division of Infectious Diseases-Regina (Lee), University of Saskatchewan; Saskatchewan Health Authority (Lee), Saskatoon, Sask.; Medical Affair and Innovation (Lewin), Héma-Québec, Montréal, Que.; Departments of Epidemiology and Community Medicine (O'Brien), and Pathology and Laboratory Medicine (Pambrun), Faculty of Medicine, University of Ottawa, Ottawa, Ont.; Department of Mathematics & Statistics (Stephens), McGill University, Montréal, Que.; Department of Medical Microbiology (Stein, Van Caeseele), University of Manitoba, and Cadham Provincial Laboratory, Winnipeg, Man.; School of Population and Global Health (Evans), McGill University; The Research Institute of the McGill University Health Centre (Mazer, Buckeridge), Montréal, Que. david.buckeridge@mcgill.ca bruce.mazer@mcgill.ca.

PMID: 37580072
PMCID: PMC10426348
DOI: 10.1503/cmaj.230249

Abstract

Background: During the first year of the COVID-19 pandemic, the proportion of reported cases of COVID-19 among Canadians was under 6%. Although high vaccine coverage was achieved in Canada by fall 2021, the Omicron variant caused unprecedented numbers of infections, overwhelming testing capacity and making it difficult to quantify the trajectory of population immunity.

Methods: Using a time-series approach and data from more than 900 000 samples collected by 7 research studies collaborating with the COVID-19 Immunity Task Force (CITF), we estimated trends in SARS-CoV-2 seroprevalence owing to infection and vaccination for the Canadian population over 3 intervals: prevaccination (March to November 2020), vaccine roll-out (December 2020 to November 2021), and the arrival of the Omicron variant (December 2021 to March 2023). We also estimated seroprevalence by geographical region and age.

Results: By November 2021, 9.0% (95% credible interval [CrI] 7.3%-11%) of people in Canada had humoral immunity to SARS-CoV-2 from an infection. Seroprevalence increased rapidly after the arrival of the Omicron variant - by Mar. 15, 2023, 76% (95% CrI 74%-79%) of the population had detectable antibodies from infections. The rapid rise in infection-induced antibodies occurred across Canada and was most pronounced in younger age groups and in the Western provinces: Manitoba, Saskatchewan, Alberta and British Columbia.

Interpretation: Data up to March 2023 indicate that most people in Canada had acquired antibodies against SARS-CoV-2 through natural infection and vaccination. However, given variations in population seropositivity by age and geography, the potential for waning antibody levels, and new variants that may escape immunity, public health policy and clinical decisions should be tailored to local patterns of population immunity.

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Conflict of interest statement

Competing interests: Maureen Anderson reports receiving a Saskatchewan Health Research Foundation Establishment Grant, in support of the present manuscript. Lesley Behl reports receving funding from the CITF via a research grant paid to the University of Saskatchewan, in support of the present manuscript. Patrick Brown reports receiving grant support from the CITF. Carmen Charlton reports receiving grant funding from Merck and support for attending meetings or travel from AMMI Canada. Karen Colwill reports receiving an honorarium for a presentation to the Ontario Society of Clinical Chemists. Dr. Colwill is also the vice president of communications for the Canadian National Proteomics Network. Tim Evans reports receiving support for the present manuscript from the CITF, and holds the role of its executive director. Anne-Claude Gingras reports receiving support for automated equipment for ELISA, housed at the Lunenfeld-Tanenbaum Research Institute (a facility supported by Canada Foundation for Innovation funding, the Ontario Government, Genome Canada and Ontario Genomics); support from the Canadian Institutes of Health Research (CIHR) for general lab operations; salary support as a Canada Research Chair (Tier 1) in functional proteomics; and from CITF and the Public Health Agency of Canada (PHAC) for assay calibration at Mount Sinai, all in support of the present manuscript. Dr. Gingras has had a contract with Providence Therapeutics (no consultation fees received), and has received grant funding from CIHR for several SARS-CoV-2 studies and from the Ontario Research Fund, outside of the present work. Dr. Gingras has served as the chair of the Institute Advisory Board of the CIHR Institute of Genetics and is a member and chair of the Human Health Therapeutics Division advisory board, National Research Council of Canada. Dr. Gingras is a member of the CITF working parties on testing and immunology, and is pillar lead of the Functional Genomics and Structure Function of CoVaRR-Net (all roles unpaid). Steven Drews reports receiving grants or contracts from CIHR and Alberta Innovates, consulting fees from Roche, support for attending meetings or travel from the Canadian Immunization Research Network and other support from Abbott. Jaspreet Jain reports receiving support from the CITF for the present manuscript. Prabhat Jha reports receiving grant support from the CITF for the Action to Beat Coronavirus study. Amanda Lang reports receiving funding from the CITF, in support of the present manuscript, for assay reagents and technologist salary. Dr. Lang has also received support from the CITF to attend a CITF meeting. Stephen Lee reports receiving funding from the CITF, in support of the present manuscript. Sheila O’Brien reports receiving payment (paid to Canadian Blood Services [CBS]) from the Government of Canada, and laboratory infrastructure from CBS, in support of the present manuscript. Chantale Pambrun reports receiving salary support from CBS, and study funding from PHAC. Olivia Oxlade is an employee of the CITF Secretariat. David Stephens reports receiving funds for a graduate student from the National Science and Engineering Research Council Emerging Infectious Disease Modelling, in support of the present manuscript. Hanna Swail reports receiving support from the CITF for the present manuscript. David Buckeridge reports receiving funding from PHAC, in support of the present manuscript. No other competing interests were declared.

Figures

**Figure 1:**
SARS-CoV-2 infection–acquired and vaccine–induced seroprevalence in Canada (March 2020 to March 2023). Anti-nucleocapsid (anti-N) and anti-spike (anti-S) seropositivity for all age groups combined, by region. Each point represents a seroprevalence estimate from a project at the midpoint of a sample collection period, including all age groups. Infection-acquired seropositivity was measured as anti-N or anti-S seropositivity before January 2021, but only anti-N seropositivity after December 2020. The solid and dashed black lines represent the population-weighted mean of the anti-N and anti-S seroprevalence Bayesian model estimates, respectively. The grey bands represent the 95% credible intervals. Atlantic provinces: New Brunswick, Nova Scotia, Newfoundland and Labrador, Prince Edward Island; Eastern Canada: Ontario, Quebec; Western Canada: Manitoba, Saskatchewan, British Columbia, Alberta, the Northwest Territories.

**Figure 2:**
SARS-CoV-2 infection–acquired and vaccine–induced seroprevalence (March 2020 to March 2023). Anti-nucleocapsid (anti-N) and anti-spike (anti-S) seropositivity estimates by province and sample type. Each point represents a seroprevalence estimate from a project at the midpoint of a sample collection period. The solid and dashed black lines represent the average anti-N and anti-S seroprevalence, respectively, estimated from a Bayesian hierarchical model that accounts for sample size. The grey bands represent the 95% credible intervals. See the Methods section for details of the statistical model. Note: PT = provincial and territorial.

**Figure 3:**
SARS-CoV-2 infection–acquired seroprevalence. Anti-nucleocapsid (anti-N) seropositivity estimates by age group (March 2020 to March 2023). Each age-stratified seroprevalence estimate reported is plotted both at the centre of the age stratum and the midpoint of the temporal sampling interval. Each estimate is plotted at the midpoint of the sample collection period and coloured for the corresponding age group. The coloured trend lines represent the average anti-N seroprevalence estimated from a Bayesian hierarchical model that accounts for sample size. The coloured bands represent the 95% credible intervals. See the Methods section for details of the statistical model.

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[9] Colwill K, Galipeau Y, Stuible M, et al. . A scalable serology solution for profiling humoral immune responses to SARS-CoV-2 infection and vaccination. Clin Transl Immunology 2022;11:e1380. - PMC - PubMed

[10] Colwill K, Galipeau Y, Stuible M, et al. . A scalable serology solution for profiling humoral immune responses to SARS-CoV-2 infection and vaccination. Clin Transl Immunology 2022;11:e1380. - PMC - PubMed

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The evolution of SARS-CoV-2 seroprevalence in Canada: a time-series study, 2020-2023

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The evolution of SARS-CoV-2 seroprevalence in Canada: a time-series study, 2020-2023

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