Active Surveillance for Myocarditis and Pericarditis in Canadian Children from 2021 to 2022: A Canadian Immunization...

Area of Science:

• Pediatric Cardiology
• Vaccine Safety Surveillance
• Infectious Disease Epidemiology

Background:

• Myocarditis, myopericarditis, and pericarditis are inflammatory conditions of the heart muscle and surrounding sac.
• Understanding the relationship between COVID-19 vaccination and these conditions in children is crucial for public health guidance.

Purpose of the Study:

• To compare the characteristics of pediatric myocarditis, myopericarditis, and pericarditis cases based on COVID-19 vaccination status.
• To evaluate the association between COVID-19 mRNA vaccination and the incidence of these cardiac conditions in children.

Main Methods:

• Active surveillance was conducted through the Canadian Immunization Monitoring Program Active (IMPACT) network from June 2021 to December 2022.
• Cases of myocarditis, myopericarditis, and pericarditis in children ≤16 years were identified and analyzed.
• Characteristics were compared between vaccine-proximate, remotely vaccinated, and unvaccinated groups using a self-controlled case series analysis.

Main Results:

• 168 pediatric cases were identified; 73 were vaccine-proximate, 47 remotely vaccinated, and 39 unvaccinated.
• Vaccine-proximate cases predominantly affected males aged 12-16 years.
• Unvaccinated cases showed a higher likelihood of requiring intensive care unit admission (28% vs. <7%).
• The adjusted relative incidence of myocarditis/myopericarditis/pericarditis within 0-21 days post-vaccination was 7.1.

Conclusions:

• COVID-19 mRNA vaccination is associated with an increased relative incidence of myocarditis, myopericarditis, and pericarditis in children.
• Despite the association, children experiencing these conditions following vaccination appeared to have a less severe clinical course compared to unvaccinated children.