SARS-CoV-2 mRNA vaccination was associated with an increased incidence of myocarditis within 7 days (0.97 cases per 100,000 doses; observed-to-expected ratio 14.81, 95% CI 10.83-16.55).
Cohort
Does any dose of an mRNA vaccine against SARS-CoV-2 increase the incidence of hospital admission or emergency department visit for myocarditis or myopericarditis in the general population?
mRNA vaccination against SARS-CoV-2 is associated with a higher than expected rate of myocarditis, particularly in males aged 18-29 years receiving a second dose of the mRNA-1273 vaccine.
Effect estimate: Observed-to-expected ratio 14.81 (95% CI 10.83-16.55)
BACKGROUND: Postmarketing evaluations have linked myocarditis to SARS-CoV-2 mRNA vaccines. We sought to estimate the incidence of myocarditis after mRNA vaccination against SARS-CoV-2, and to compare the incidence with expected rates based on historical background rates in British Columbia. METHODS: We conducted an observational study using population health administrative data from the BC COVID-19 Cohort from Dec. 15, 2020, to Mar. 10, 2022. The primary exposure was any dose of an mRNA vaccine against SARS-CoV-2. The primary outcome was incidence of hospital admission or emergency department visit for myocarditis or myopericarditis within 7 and 21 days postvaccination, calculated as myocarditis rates per 100 000 mRNA vaccine doses, expected rates of myocarditis cases and observedto-expected ratios. We stratified analyses by age, sex, vaccine type and dose number. RESULTS: We observed 99 incident cases of myocarditis within 7 days (0.97 cases per 100 000 vaccine doses; observed v. expected ratio 14.81, 95% confidence interval CI 10.83-16.55) and 141 cases within 21 days (1.37 cases per 100 000 vaccine doses; observed v. expected ratio 7.03, 95% CI 5.92-8.29) postvaccination. Cases of myocarditis per 100 000 vaccine doses were higher for people aged 12-17 years (2.64, 95% CI 1.54-4.22) and 18-29 years (2.63, 95% CI 1.94-3.50) than for older age groups, for males compared with females (1.64, 95% CI 1.30-2.04 v. 0.35, 95% CI 0.21-0.55), for those receiving a second dose compared with a third dose (1.90, 95% CI 1.50-2.39 v. 0.76, 95% CI 0.45-1.30) and for those who received the mRNA-1273 (Moderna) vaccine compared with the BNT162b2 (Pfizer-BioNTech) vaccine (1.44, 95% CI 1.06-1.91 v. 0.74, 95% CI 0.56-0.98). The highest observed-to-expected ratio was seen after the second dose among males aged 18-29 years who received the mRNA-1273 vaccine (148.32, 95% CI 95.03-220.69). INTERPRETATION: Although absolute rates of myocarditis were low, vaccine type, age and sex are important factors to consider when strategizing vaccine administration to reduce the risk of postvaccination myocarditis. Our findings support the preferential use of the BNT162b2 vaccine over the mRNA-1273 vaccine for people aged 18-29 years.
Naveed et al. (Sun,) conducted a cohort in Myocarditis after SARS-CoV-2 vaccination. SARS-CoV-2 mRNA vaccine vs. Historical background rates was evaluated on Incidence of hospital admission or emergency department visit for myocarditis or myopericarditis within 7 and 21 days postvaccination (Observed-to-expected ratio 14.81, 95% CI 10.83-16.55). SARS-CoV-2 mRNA vaccination was associated with an increased incidence of myocarditis within 7 days (0.97 cases per 100,000 doses; observed-to-expected ratio 14.81, 95% CI 10.83-16.55).