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Myocarditis Following Coronavirus Disease 2019 mRNA Vaccine: A Case Series and Incidence Rate Determination
Yalile Perez1, Emily R Levy2,3, Avni Y Joshi4
1Department of Pediatric and Adolescent Medicine, Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota, USA.
Insights
Myocarditis is a rare side effect of COVID-19 mRNA vaccines, particularly in adult males. This study found a higher incidence rate of vaccine-associated myocarditis compared to the general population.
Area of Science:
- Cardiology
- Vaccinology
- Public Health
Background:
- Myocarditis following COVID-19 mRNA vaccines is increasingly reported.
- Accurate incidence rates are needed to balance vaccination risks.
- Previous estimates used pericarditis codes, potentially underestimating myocarditis background rates.
Purpose of the Study:
- To determine the incidence rate ratio (IRR) of myocarditis following COVID-19 mRNA vaccination.
- To compare vaccine-associated myocarditis rates with background rates.
- To describe clinical characteristics and outcomes of affected individuals.
Main Methods:
- Retrospective case series using the Mayo Clinic COVID-19 Vaccine Registry.
- Comparison of myocarditis incidence in vaccinated individuals versus a 2016-2020 population.
- Identification of cases temporally related to COVID-19 mRNA vaccination.
Main Results:
- The overall IRR for COVID-19-related myocarditis was 4.18, driven by adult males (IRR 6.69).
- All cases occurred within two weeks of vaccination, mostly after the second dose.
- Identified cases were mild with full patient survival.
Conclusions:
- Myocarditis is a rare adverse event linked to COVID-19 mRNA vaccines.
- Adult males exhibit a significantly higher incidence of vaccine-associated myocarditis.
- Recurrence of myocarditis after subsequent vaccine doses remains unknown.
Background:
Myocarditis following coronavirus disease 2019 (COVID-19) mRNA vaccines (Pfizer-BioNTech and Moderna) has been increasingly reported. Incidence rates in the general population are lacking, with pericarditis rather than myocarditis diagnostic codes being used to estimate background rates. This comparison is critical for balancing the risk of vaccination with the risk of no vaccination.
Methods:
A retrospective case series was performed using the Mayo Clinic COVID-19 Vaccine Registry. We measured the incidence rate ratio (IRR) for myocarditis temporally related to COVID-19 mRNA vaccination compared with myocarditis in a comparable population from 2016 through 2020. Clinical characteristics and outcomes of the affected patients were collected. A total of 21 individuals were identified, but ultimately 7 patients met the inclusion criteria for vaccine-associated myocarditis.
Results:
The overall IRR of COVID-19-related myocarditis was 4.18 (95% confidence interval [CI], 1.63-8.98), which was entirely attributable to an increased IRR among adult males (IRR, 6.69; 95% CI, 2.35-15.52) compared with females (IRR 1.41; 95% CI, .03-8.45). All cases occurred within 2 weeks of a dose of the COVID-19 mRNA vaccine, with the majority occurring within 3 days (range, 1-13) following the second dose (6 of 7 patients, 86%). Overall, cases were mild, and all patients survived.
Conclusions:
Myocarditis is a rare adverse event associated with COVID-19 mRNA vaccines. It occurs in adult males with significantly higher incidence than in the background population. Recurrence of myocarditis after a subsequent mRNA vaccine dose is not known at this time.
