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

Zinszer K, Charland K, Pierce L, Saucier A, McKinnon B, Hamelin MÈ, Cheriet I, Da Torre MB, Carbonneau J, Nguyen CT, De Serres G, Papenburg J, Boivin G, Quach C. Pre-Omicron seroprevalence, seroconversion, and seroreversion of infection-induced SARS-CoV-2 antibodies among a cohort of children and teenagers in Montreal, Canada. Int J Infect Dis. 2023 Mar 22:S1201-9712(23)00115-7. doi:

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

A CITF-funded study, published in the International Journal of Infectious Diseases, found that seroprevalence among children and adolescents in Montreal was 5.8% pre-Omicron (October 2020 to April 2021), spiking to 11.0% during the Omicron era (November 2021 until March 2022). Higher infection rates were observed among females, those whose parents identify as a racial or ethnic minority, and those living in households with incomes less than $100,000. This study was led by Drs. Kate Zinszer and Caroline Quach-Thanh (Université de Montréal).

Key findings:

  • Participants from the West Island region of Montreal, which is generally more affluent and tends to have higher education levels, consistently had lower infection-acquired seropositivity than those in Montreal North, which is a less affluent and more racially diverse neighbourhood.
  • Infection-acquired antibodies (IgG) waned to the point of being undetectable after 7.5 months (median time to seroreversionBecoming negative for SARS-CoV-2 antibody after previously been positive). The likelihood of remaining seropositive after one year was 41%.

The increase in seroprevalence observed in the general population, including children and adolescents, in Montreal was consistent with studies in other regions of Canada. This study corroborates others suggesting the impact of the pandemic has had a consistently disproportionate impact on racial and ethnic communities and lower income households.

In addition, the study highlighted that most of the children and adolescents who participated and who had had COVID-19 did not know they had been infected. Of the 194 who had infection-acquired antibodiesThe development of antibodies specific to the virus, typically occurs within two to three weeks after symptom onset., 137 (71%) had never had a prior positive PCR or antigen test. The researchers state this indicates the importance of serological monitoring of SARS-CoV-2, highlighting that serological studies provide valuable information for infection prevalence estimates to help inform public health decision making.

Children and adolescents were recruited through daycares and schools in four different neighbourhoods of Montreal to reflect diversity in terms of geography, cumulative COVID-19 cases, and neighborhood socioeconomic status. Three rounds of data collection included questionnaires and dried blood spots.