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

Zinszer K, Charland K, Pierce L, Saucier A, McKinnon B, Hamelin M-E, Cheriet I, Da Torre MB, Carbonneau J, Nguyen CT, De Serres G, Papenburg J, Boivin G, Quach C. Seroprevalence, seroconversion, and seroreversion of infection-induced SARS-CoV-2 antibodies among a cohort of children and adolescents in Montreal, Canada. medRxiv 2022 Oct 10. doi:

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

In a preprint, not yet peer-reviewed, CITF-funded researchers Drs. Kate Zinszer (University of Montreal) and Caroline Quach (University of Montreal, Research Centre of the Sainte-Justine University Hospital) identified a variety of factors that contributed to an increased risk of seropositivity and seroconversion in children and adolescents. These included being from a racial or ethnic minority group, with high bedroom density, and/or having a lower household income. They reported, as well, that infection-acquired SARS-CoV-2 seroprevalence among children increased during the study period from 5.8% (October 2020 – March 2021) to 10.5% (May – July 2021) and 10.9% (November 2021 – January 2022).

Key findings:

  • Participants in the 5- to 11-year-old age groups whose parents identified as a racial or ethnic minority, who lived in homes with a higher number of people in each bedroom, and who had a “lower” household income (below $100,000), tended to have higher seroprevalence.
  • The average rate of seroconversion (time to first seropositive test) was 12.7 per 100 person-yearsThe rate of seroconversion means that if we follow 100 children over 1 year, 12.7 will become positive for antibodies after a SARS-CoV-2 infection.. Between May and July 2021 (round 2), more children became seropositive over a year: the rate was 15.7 per 100 person-years. Between November 2021 and January 2022 (round 3 – most samples collected before the spread of Omicron), the rate dropped down to 11.2 per 100 person-years.
  • Among children who tested positive for SARS-CoV-2 antibodies during the study period via a dried blood spot test, 71% had not had a positive RT-PCR or rapid antigen test. This suggests that reported/self-reported RT-PCR and rapid antigen test results underestimate true disease prevalence.
  • Children have antibodies against SARS-CoV-2 for a median time of 7.5 months, and then these antibodies do not become detectable, indicating waning of immunity against SARS-CoV-2.

Serological studies provide valuable infection prevalence estimates in children and adolescents to inform public health recommendations including COVID-19 vaccination and booster schedules.

This study reported on three rounds of data collection from a prospective cohort study (Enfants et COVID-19: Étude de séroprévalence [EnCORE]) of children and adolescents aged 2 to 17 years in Montreal, Canada. Most of the third round of samples were collected prior to the spread of the Omicron BA.1 variant. The study included dried blood spot samples from 1,632, 936, and 723 participants in the first, second, and third rounds of data collection, respectively.