Active Surveillance for Myocarditis and Pericarditis in Canadian Children from 2021 to 2022: A Canadian Immunization Monitoring Program ACTive Study

Karina A Top; Julie A Bettinger; Joanne E Embree; Taj Jadavji; Rupeena Purewal; Laura Sauvé; Jesse Papenburg; Shelley L Deeks; Sarah E Wilson; Nagib Dahdah; Manish Sadarangani; Scott A Halperin; Fatima Kakkar; Shaun K Morris; IMPACT Investigators

doi:10.1016/j.jpeds.2025.114642

Active Surveillance for Myocarditis and Pericarditis in Canadian Children from 2021 to 2022: A Canadian Immunization Monitoring Program ACTive Study

J Pediatr. 2025 May 13:284:114642. doi: 10.1016/j.jpeds.2025.114642. Online ahead of print.

Authors

Collaborators

IMPACT Investigators:
Natalie Bridger, Jeannette Comeau, Roseline Thibeault, Marc Lebel, Nicole Le Saux, Kescha Kazmi, Jeffrey M Pernica, Jared Bullard, Rupesh Chawla, Cora Constantinescu, Catherine Burton

Affiliations

¹ Faculty of Medicine, Dalhousie University, and Canadian Center for Vaccinology, IWK Health, Halifax, NS, Canada; Department of Pediatrics and Li Ka Shing Institute of Virology, University of Alberta, Edmonton, AB, Canada. Electronic address: ktop@ualberta.ca.
² Vaccine Evaluation Center, BC Children's Hospital Research Institute, University of British Columbia, Vancouver, BC, Canada; Division of Infectious Diseases, Department of Pediatrics, BC Children's Hospital, University of British Columbia, Vancouver, BC, Canada.
³ Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, MB, Canada.
⁴ Division of Pediatric Infectious Diseases, Alberta Children's Hospital, University of Calgary, Calgary, AB, Canada.
⁵ Division of Paediatric Infectious Diseases, Jim Pattison Children's Hospital, Saskatchewan Health Authority, Saskatoon, SK, Canada.
⁶ Division of Pediatric Infectious Diseases, Montreal Children's Hospital, McGill University, Montreal, QC, Canada.
⁷ Faculty of Medicine, Dalhousie University, and Canadian Center for Vaccinology, IWK Health, Halifax, NS, Canada; Nova Scotia Department of Health and Wellness, Halifax, NS, Canada.
⁸ Public Health Ontario and Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
⁹ Division of Pediatric Cardiology, Centre Hospitalier Universitaire Sainte-Justine and Université de Montréal, Montreal, QC, Canada.
¹⁰ Faculty of Medicine, Dalhousie University, and Canadian Center for Vaccinology, IWK Health, Halifax, NS, Canada.
¹¹ Division of Infectious Diseases, Centre Hospitalier Universitaire Sainte-Justine, Montreal, Canada.
¹² Division of Infectious Diseases, The Hospital for Sick Children, Toronto, ON, Canada; Child Health Evaluative Sciences and the Center for Global Child Health, The Hospital for Sick Children, Toronto, ON, Canada.

PMID: 40373954
DOI: 10.1016/j.jpeds.2025.114642

Abstract

Objective: To compare characteristics of children assessed at Canadian Immunization Monitoring Program Active (IMPACT) centers for myocarditis, myopericarditis, and pericarditis according to COVID-19 vaccination status, and to evaluate the association with vaccination.

Study design: IMPACT conducted active surveillance for myocarditis, myopericarditis, and pericarditis by monitoring admission lists and diagnostic codes for children ≤16 years of age assessed in emergency departments or hospitalized with these conditions (June 2021 through December 2022). Clinical details and immunization histories were entered in an electronic database. Characteristics of cases meeting Brighton Collaboration case definitions for myocarditis and/or pericarditis were compared between COVID-19 mRNA vaccine-proximate (vaccination 0-21 days prior to presentation), remotely vaccinated (vaccinated >21 days prior), and unvaccinated cases. Relative incidence of myocarditis/myopericarditis/pericarditis 0-21 days after vaccination was estimated via a self-controlled case series analysis adjusted for pre-Omicron vs Omicron periods. Cell sizes <5 were suppressed.

Results: Overall, 168 cases were included: 73 (43%) vaccine-proximate cases, 47 (28%) remotely vaccinated, 39 (23%) unvaccinated, and 9 (5%) with unknown vaccination status. Among vaccine-proximate cases, 88% (64/73) were male, and 95%-99% (69-72/73) were 12-16 years of age. Among unvaccinated cases, 56% (22/39) were male, and 36% (14/39) were 12-16 years of age. Unvaccinated cases appeared more likely to require intensive care unit care (28% vs <7% of vaccine-proximate cases). The adjusted relative incidence of myocarditis/myopericarditis/pericarditis 0-21 days postvaccination was 7.1 (95% CI 4.5-11.1).

Conclusions: Although myocarditis, myopericarditis, and pericarditis were associated with COVID-19 mRNA vaccination, children with postvaccine myocarditis, myopericarditis, and pericarditis appeared to have a less severe initial course than unvaccinated children.

Keywords: COVID-19 mRNA vaccine; SARS-CoV-2; adverse event following immunization; vaccination.