This is a summary, written by members of the CITF Secretariat, of the four presentations given at the CITF Scientific Meeting in Vancouver, March 8-10, 2023, during the breakout session entitled, Seroprevalence and effects of COVID-19 on children and adolescents.

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

Ongoing monitoring of the serological status of children is important, particularly in the context of new variants of concern, low vaccine coverage, and low uptake of testing. Here, members of the CITF Secretariat summarize results from the four presentations given during the breakout session, “Seroprevalence and effects of COVID-19 on children and adolescents,” at the CITF Scientific Meeting in Vancouver, March 8-10, 2023.

  1. Presenter and CITF PI Dr. Stephen Freedman and CITF PI Dr. Roger Zemek: A comparison of profiles among children infected by SARS-CoV-2 variants: A pan-Canadian prospective cohort study

As SARS-CoV-2 has evolved, so have symptoms and disease severity, but still little is known about disease severity in children. The study quantifies and compares symptoms, emergency department (ED) chest x-rays, treatments, and disposition across dominant SARS-CoV-2 variants in a prospective ED-based cohort study in Canada.

Key findings:

  • Omicron and Delta variants were more strongly associated with fever and cough.
  • Alpha variant had fewer symptoms than other variants of concern (VOC).
  • Children with Omicron infections were more likely to undergo testing, receive treatment and revisit the ED. They were more likely to:
    1. report lower respiratory tract symptoms and systemic manifestations
    2. need chest radiography
    3. receive interventions
  • Although presenting symptoms have changed as the virus has evolved, the proportions of children experiencing undesirable outcomes have remained stable (unlike in adults).

The study recruited children (<18 years old) who were tested for acute SARS-CoV-2 infection and presented for care at one of 14 PERC (Pediatric Emergency Resesarch Canada) EDs from August 4, 2020 to February 22, 2022.

  1. Presenter Ms. Laura Pierce and CITF PI Dr. Kate Zinszer: Seroprevalence, seroconversion, and seroreversion of infection-acquired SARS-CoV-2 antibodies among a cohort of children and youth in Montreal, QC

The study estimated seroprevalence, seroconversion, and seroreversion of infection-acquired SARS-CoV-2 antibodies in over 4000 samples collected from October 2020 to October 2022 in children from 2- to 18-years-old.

Key findings:

  • Infection-acquired seroprevalence rose from 5.8% between October 2020-April 2021 to 58.4% between May-October 2022, reflecting the emergence of new variants over time.
  • Infection-acquired seroprevalence was higher in children in racialized and ethnic minorities than in the white population throughout the study (October 2020-October 2022).
  • After the emergence of Omicron, the seroconversion rate (the rate of becoming seropositive for SARS-CoV-2 infection) was 9-12 times higher than in the previous rounds of data collection.
  1. Presenter Mrs. Marina Vineta and CITF PI Dr. Pascal Lavoie: Immunogenicity of BNT162b2 SARS-CoV-2 vaccine in pediatric inflammatory bowel disease patients treated with biologic therapy

The study evaluated the long-term immunogenicity of the SARS-CoV-2 vaccine in pediatric patients with inflammatory bowel disease (IBD) who were treated with anti-TNF-α therapy in monotherapy or anti-TNF-α in combination with immunomodulators, compared to vedolizumab therapy. This prospective study recruited children aged 5-18 years with IBD at BC Children’s Hospital.

Key findings:

  • Pediatric IBD patients generated a strong response to SARS-CoV-2 vaccines regardless of the type of immunosuppressive therapy they received.
  • Booster doses promoted an increase in antibody levels.
  • There was no difference between the monotherapy and combination therapy groups in the levels of spike IgG antibodies against the Omicron BA.4-BA.5 variant.

Overall, despite initial concerns about the potential for poor SARS-CoV-2 responses related to immune suppression, children with IBD treated with biological therapy responded well to complete SARS-CoV-2 vaccination and were not hospitalized due to COVID-19.

  1. Presenter Ms. Mary Aglipay and CITF PI Dr. Jonathon Maguire: Seroprevalence of SARS-CoV-2 antibodies among children in the Greater Toronto Area

This study describes the seroprevalence of infection-acquired and vaccine-induced antibodies among children aged six months-18 years recruited from TARGet Kids! in the Greater Toronto Area from January 2021 to November 2022.

Key findings:

  • Infection-acquired seroprevalence was 44% among participants, while overall infection-acquired and vaccine-induced seroprevalence was 74% from July-Nov 2022.
  • Discernable differences by age, income, education, ethnicity, and household density were observed in the seroprevalence of vaccine-induced antibodies, but not for infection-acquired antibodies.
  • Children from ethnic minorities had higher infection-acquired seroprevalence than children of European descent (55.6% vs. 42.9%).