Peer-reviewed article

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

Kate Zinszer, Britt McKinnon, Noémie Bourque, Laura Pierce, Adrien Saucier et al. · 23 Nov 2021

Summary

Written by AI, not yet AICS's view · claude-haiku-4-5-20251001

This study measured how many children in Montreal had been exposed to SARS-CoV-2 by testing for antibodies in blood samples collected between October 2020 and March 2021. About 1,632 children aged 2 to 17 from day cares and schools participated. The findings show that 5.8% of children had antibodies, meaning they had been infected, though most had mild or no symptoms. Children from racial and ethnic minority families were nearly twice as likely to show evidence of prior infection.

Key points

Seroprevalence increased from 3.2% in October-November 2020 to 8.4% by March-April 2021
Of 95 seropositive children, 82% had not been detected by standard RT-PCR testing
All seropositive children experienced only mild or no clinical symptoms
Children of parents identifying as racial or ethnic minorities had 1.9 times higher seroprevalence than White children
The study suggests more transmission occurred in children than detected by routine testing

Limitations

This was a convenience sample from Montreal only, predominantly from families with higher education levels, and cannot represent all Canadian children or generalise to other regions. The study provides a snapshot of exposure but does not evaluate health outcomes or the effectiveness of any intervention to protect child health.

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.