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

Silverberg SL, Shulha HP, McMillan B, He G, Lee A, Márquez AN, 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 severe acute respiratory syndrome-related coronavirus 2 infection in unvaccinated children and young adults. medRxiv. 18 Aug 2023; 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A CITF-funded study, published as a preprint and not yet peer-reviewed, found that the highest seropositivity rates among unvaccinated youth were among children under four years old and young adults aged 20-24. This was evident even though school-aged children had returned to in-person schooling. Among unvaccinated participants of all ages in this study, those of South Asian descent had a higher seropositivity rate than other ethnic groups (13.5% vs. 5.2%). This study was led by Dr. Manish Sadarangani in collaboration with Dr. Julie Bettinger (both from University of British Columbia), Dr. Agatha Jassem, Dr. Muhammad Morshed, Dr. Mel Krajden (all three from BC Centre for Disease Control).

A total of 2,864 unvaccinated children and young adults less than 25 years of age were recruited for this study in British Columbia.

Key findings:

  • Infection-acquired seropositivity was highest between January 2022 to May 2022, during the emergence of the Omicron variant, compared to the ancestral, pre-Delta, and Delta periods between November 2020 and December 2021.
  • Unvaccinated young children under four years of age and young adults ages 20 to 24 had the highest reported infection-acquired seropositivity levels (7.0% and 7.2% respectively vs. 3.0-5.6% across other age groups from 4 to 19 years of age).
  • South Asian participants were disproportionally affected showing higher infection-acquired seropositivity levels than other ethnic groups (13.5% vs. 5.2%).
  • Individuals who had travelled internationally had a higher seropositivity than those who had travelled within Canada or did not travel (7.7% vs 5.1%).

Though the authors stress that vaccination among children and young adults remains important, their data provide additional reassurance that widespread transmission did not occur among susceptible children through much of the pandemic despite continued in-person activities. This is in part due to preventive interventions (such as masking and distancing) that enabled safer social and educational activities.

Their findings, the research team states, underscore the importance of continued surveillance and reporting mechanisms that account for age-dependent infection and disease to understand pandemic dynamics and track epidemiological changes in SARS-CoV-2 variants.

The study included two cross-sectional serosurveys. Phase 1 enrolled children and adults younger than 25 years old between November 2020 and May 2021 and phase 2 enrolled children younger than 10 years old between June 2021 and May 2022. Participants completed electronic surveys and self-collected finger-prick dried blood spot (DBS) samples. In BC, COVID-19 vaccines were generally available for adults aged over 18 years from April 2021, adolescents aged 12-17 years from May 2021, children aged 5-11 years from November 2021, and for younger children ages 6 months to 5 years from August 2022.