Epidemiology of Myocarditis and Pericarditis Following mRNA Vaccination by Vaccine Product, Schedule, and Interdose Interval Among Adolescents and Adults in Ontario, Canada.
Level 3 - non-randomized controlled study
Population-based retrospective cohort study using registry and surveillance data
PubMed 35749115 · doi:10.1001/jamanetworkopen.2022.18505
What was done
This population-based cohort study analyzed data from Ontario's COVID-19 vaccine registry and passive vaccine-safety surveillance system from December 14, 2020, to September 4, 2021. Individuals receiving at least 1 dose of mRNA COVID-19 vaccine (mRNA-1273 or BNT162b2) were included. Reported myocarditis or pericarditis cases meeting Brighton Collaboration levels 1 to 3 definitions were identified. Rates per 1,000,000 administered doses with 95% CIs were estimated across age, sex, dose number, vaccine product, and interdose interval.
What was found
Among 19,740,741 mRNA vaccine doses administered, 297 cases of myocarditis or pericarditis met inclusion criteria. Of these, 228 (76.8%) occurred in males (median age 24 years, range 12–81) and 207 (69.7%) followed dose 2. Under enhanced passive surveillance (on or after June 1, 2021), males aged 18 to 24 years had the highest post-dose 2 rate with mRNA-1273 (299.5 per 1,000,000 doses; 95% CI, 171.2–486.4) compared to BNT162b2 (59.2 per 1,000,000 doses; 95% CI, 19.2–138.1). Interdose intervals of 30 or fewer days had higher rates than intervals of 56 or more days for both BNT162b2 (52.1 vs 9.6 per 1,000,000 doses) and mRNA-1273 (83.9 vs 16.2 per 1,000,000 doses).
Why it matters
The findings show that post-mRNA vaccine myocarditis/pericarditis risk was elevated in young males, with mRNA-1273 second doses, and with shorter interdose intervals. This provides actionable evidence that extending interdose intervals and product selection can reduce cardiac risks in vaccination campaigns.
Limits
The study relied on a passive vaccine-safety surveillance system, which is subject to underreporting and reporting bias. Surveillance intensity changed over time (enhanced surveillance began June 2021), potentially affecting rate comparisons across time periods. Confounders influencing interdose interval timing and long-term clinical outcomes were not detailed in the abstract.
Cited by
- context COVID-19 vaccination caused myocarditis in young people at a rate of 1 in 5,000 to 1 in 10,000.