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

Silverberg SL, Shulha HP, McMillan B, He G, Lee A, Márquez AC, Bartlett SR, Gill V, Abu-Raya B, Bettinger JA, Cabrera A, Coombs D, Gantt S, Goldfarb DM, Sauvé L, Krajden M, Morshed M, Sekirov I, Jassem AN, Sadarangani M. Factors associated with SARS-CoV-2 infection in unvaccinated children and young adults. BMC Infectious Diseases. 2024 January 15. 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 BMC Infectious Diseases, aimed to determine age-specific population SARS-CoV-2 seropositivity and identify risk factors for infection among unvaccinated children and young adults. The researchers found that SARS-CoV-2 seropositivity was highest among infants and children under five years old and young adults, compared to school-aged children. Overall, South Asian participants had a higher seropositivity than other ethnicities. This study was led by Dr. Sarah L. Silverberg (The Hospital for Sick Children) and Dr. Manish Sadarangani (University of British Columbia) in collaboration with Dr. Agatha Jassem (University of British Columbia).

The study involved a total of 2,864 unvaccinated participants in two phases. Phase 1 enrolled children and adults under 25 years old from November 2020 to May 2021 and Phase 2 enrolled children under 10 years old from May 2021 to May 2022. All participants completed surveys that documented socio-demographic data, potential SARS-CoV-2 exposures, respiratory symptoms since January 2020, COVID-19 diagnoses, travel history, and infection prevention and control behaviours. They also provided dried blood spot (DBS) samples for IgG detection.

Key findings:

  • Overall, seropositivity was 5.5% across both phases and was highest for infants and children under five years and young adults aged 20–24, at 7% and 7.2%, respectively.
  • Those who had travelled internationally since January 2020 had higher seropositivity compared to those who had travelled within Canada or not travelled at all (7.7% versus 5.1%).
  • Within Phase 2, specifically from January to May 2022, seropositivity was highest among children aged 0–4 years and 5–9 years at 21.9% and 60%, respectively, likely spiking due to the spread of the Omicron variant.
  • Among all ethnic groups, South Asians had the highest seropositivity at 13.5%, compared to 2.8% (Chinese), 4.8% (White), 5.7% (mixed), and 6.6% (other).

This study of unvaccinated children and young adults, largely representative of the various ethnicities in British Columbia, shows that seropositivity was low in 2021, despite returns to in-person schooling. It increased in early 2022 with the advent of the Omicron variant. There were low rates of missing data for core demographics and the DBS assay had good sensitivity for detecting antibodies to SARS-CoV-2. However, some northern and Indigenous communities were underrepresented, and the study was not able to capture changes in seropositivity over time.

These findings reinforce the need for improved surveillance to identify disease burden across the pediatric age range to better understand pandemic dynamics and inform policies around in-person activities for children.