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Seroprevalence of SARS-CoV-2 Antibodies Among Children in School and Day Care in Montreal, Canada

Educational Objective
To identify the key insights or developments described in this article
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Key Points

Question  What is the seroprevalence of SARS-CoV-2 antibodies in a convenience sample of children aged 2 to 17 years in Montreal, Canada, enrolled between October 2020 and March 2021?

Findings  In this cohort study of 1632 participants, the mean baseline seroprevalence of SARS-CoV-2 was 5.8%. Of the 95 participants who were seropositive for SARS-CoV-2 antibodies, 82% were not tested or tested negative, and all experienced either mild or no clinical symptoms.

Meaning  The findings suggest that there was more transmission occurring in children compared with what was being detected, although children experienced few or mild symptoms.

Abstract

Importance  Quebec prioritized in-person learning after the first wave of the COVID-19 pandemic, with school closures being implemented temporarily in selected schools or in hot-spot areas. Quebec’s decision to keep most schools open was controversial, especially in Montreal, which was the epicenter of Canada’s first and second waves; therefore, understanding the extent to which children were infected with SARS-CoV-2 provides important information for decisions about school closures.

Objective  To estimate the seroprevalence of SARS-CoV-2 antibodies in children and teenagers in 4 neighborhoods of Montreal, Canada.

Design, Setting, and Participants  This cohort study (the Enfants et COVID-19: Étude de séroprévalence [EnCORE] study) enrolled a convenience sample of children aged 2 to 17 years between October 22, 2020, and March 22, 2021, in Montreal, Canada.

Exposures  Potential exposure to SARS-CoV-2.

Main Outcomes and Measures  The main outcome was seroprevalence of SARS-CoV-2 antibodies, collected using dried blood spots (DBSs) and analyzed with a research-based enzyme-linked immunosorbent assay (ELISA). Parents also completed an online questionnaire that included questions on self-reported COVID-19 symptoms and tests, along with sociodemographic questions.

Results  This study included 1632 participants who provided a DBS sample from 30 day cares, 22 primary schools, and 11 secondary schools. The mean (SD) age of the children who provided a DBS sample was 9.0 (4.4) years; 801 (49%) were female individuals, with 354 participants (22%) from day cares, 725 (44%) from primary schools, and 553 (34%) from secondary schools. Most parents had at least a bachelor’s degree (1228 [75%]), and 210 (13%) self-identified as being a racial or ethnic minority. The mean seroprevalence was 5.8% (95% CI, 4.6%-7.0%) but increased over time from 3.2% (95% CI, 0.7%-5.8%) in October to November 2020 to 8.4% (95% CI, 4.4%-12.4%) in March to April 2021. Of the 95 children with positive SARS-CoV-2 antibody results, 78 (82%) were not tested or tested negative with reverse transcription–polymerase chain reaction (RT-PCR) testing, and all experienced mild (49 [52%]) or no clinical symptoms (46 [48%]). The children of parents who self-identified as belonging to a racial and ethnic minority group were more likely to be seropositive compared with children of White parents (adjusted seroprevalence ratio, 1.9; 95% CI, 1.1-2.6).

Conclusions and Relevance  These results provide a benchmark of the seroprevalence status in Canadian children. The findings suggest that there was more transmission occurring in children compared with what was being detected by RT-PCR, although children experienced few or mild symptoms. It will be important to continue monitoring the serological status of children, particularly in the context of new COVID-19 variants of concern and in the absence of mass vaccination campaigns targeting young children.

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Article Information

Accepted for Publication: September 29, 2021.

Published: November 23, 2021. doi:10.1001/jamanetworkopen.2021.35975

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Zinszer K et al. JAMA Network Open.

Corresponding Author: Kate Zinszer, PhD, University of Montreal School of Public Health, 7101 avenue du Parc, Montreal, QC H3N 1X9, Canada (kate.zinszer@umontreal.ca).

Author Contributions: Dr Zinszer had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Zinszer, Papenburg, Zahreddine, Haley, Conrod, De Serres, Quach.

Acquisition, analysis, or interpretation of data: Zinszer, McKinnon, Bourque, Pierce, Saucier, Otis, Cheriet, Papenburg, Hamelin, Charland, Carbonneau, Zahreddine, Savard Lamothe, Fortin, Apostolatos, Ratté, Laurin, Nguyen, Conrod, Boivin, De Serres.

Drafting of the manuscript: Zinszer, McKinnon, Bourque, Pierce, Fortin.

Critical revision of the manuscript for important intellectual content: Zinszer, McKinnon, Bourque, Pierce, Saucier, Otis, Cheriet, Papenburg, Hamelin, Charland, Carbonneau, Zahreddine, Savard Lamothe, Apostolatos, Haley, Ratté, Laurin, Nguyen, Conrod, Boivin, De Serres, Quach.

Statistical analysis: McKinnon, Charland, Apostolatos, Conrod.

Obtained funding: Zinszer, Zahreddine, Haley, De Serres, Quach.

Administrative, technical, or material support: Zinszer, McKinnon, Bourque, Pierce, Saucier, Otis, Cheriet, Hamelin, Carbonneau, Zahreddine, Savard Lamothe, Fortin, Apostolatos, Haley, Ratté, Laurin, Nguyen, Conrod, Boivin.

Supervision: Zinszer, McKinnon, Otis, Zahreddine, Boivin, De Serres.

Conflict of Interest Disclosures: Dr Papenburg reported receiving grants and personal fees from AbbVie, personal fees and nonfinancial support from Seegene, and grants from Sanofi Pasteur and MedImmune outside the submitted work. Dr Quach reported receiving grants from the Canadian Institutes of Health Research, the COVID Immunity Task Force (Public Health Agency of Canada), the Quebec Ministry of Health, and the Public Health Agency of Canada outside the submitted work. No other disclosures were reported.

Funding/Support: Funding for this study was provided by the Public Health Agency of Canada through the COVID-19 Immunity Task Force to Dr Zinszer.

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: We sincerely thank all of the children, teens, and their parents for their precious contribution to our study. We also thank all of the day cares, schools, and school boards for their help with recruitment. We are grateful for the support and guidance of our partners: the Direction régionale de santé publique de Montréal, the COVID-19 Immunity Task Force, the Institut national de santé publique du Québec, and the Observatoire pour l’éducation et la santé des enfants.

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