This is a summary, written by members of the CITF Secretariat, of:

Zinszer K, McKinnon B, Bourque N, Pierce L, Saucier A, Otis A,  Cheriet I, Papenburg J, Hamelin ME, Charland K, Carbonneau J, Zahreddine M, Savard A, Fortin G, Apostolatos A, Haley N, Ratté N, Laurin I, Nguyen  CT, Conrod P, Boivin G, De Serres G, Quach C; Seroprevalence of SARS-CoV-2 Antibodies Among Children in School and Day Care in Montreal, Canada. JAMA Network Open 4.11 (2021): e2135975-e2135975.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study by researcher Dr. Kate Zinszer from the Université de Montréal and colleagues found that SARS-CoV-2 antibodies due to infection in children aged 2 to 17 years in Montreal increased over time, from 3.2% in October-November 2020 to 8.4% in March-April 2021. This offers a benchmark for seroprevalence due to infection in children across Canada. The findings suggest that the number of infections in children may not be reflected by positive PCR tests alone, with higher true infection rates due to asymptomatic and mildly symptomatic individuals who may not have been tested. The study appears in JAMA Network Open.

Researchers collected information from 1632 children and teenagers across 30 daycares, 22 primary schools, and 11 secondary schools in Montreal between October 2020 and March 2021.

Key findings:

  • The mean baseline seroprevalence of SARS-CoV-2 was 5.8% but increased over time from 3.2% between October and November 2020 to 8.4% between March and April 2021.
  • Of the 95 participants who were seropositive for SARS-CoV-2 antibodies, 82% were either not tested for infection or tested negative by PCR.
  • All seropositive participants experienced either mild or no clinical symptoms.
  • The children of parents who self-identified as belonging to a racial or ethnic minority group were more likely to be seropositive compared with children of self-identified white parents (adjusted seroprevalence ratio, 1.9; 95% CI, 1.1-2.6).

In this cohort study, the mean age of the children who provided a dried blood spot (DBS) sample was 9 years. 49% were females. 354 participants (22%) were from day cares, 725 (44%) from primary schools, and 553 (34%) from secondary schools. Parents also completed an online questionnaire that included queries on self-reported COVID-19 symptoms and tests for COVID-19, along with sociodemographic questions.

It will be important to continue monitoring the serological status of children, particularly in the context of new COVID-19 variants of concern and pediatric vaccination.