1. In this descriptive study, the risk of myocarditis after receiving mRNA-based COVID-19 vaccines was increased across multiple age and sex strata.
2. The rates of myocarditis cases were highest after the second vaccination dose in adolescent males and in young men.
Evidence Rating Level: 3 (Average)
Study Rundown: Myocarditis is an inflammatory disease process of the myocardium that most often affects younger patients. Despite clear public health benefits of COVID-19 vaccinations, isolated case reports of myocarditis have been identified among individuals who have received the recent mRNA-based COVID-19 vaccinations. This descriptive study explored reports and confirmed cases of myocarditis reported to the Vaccine Adverse Event Reporting System (VAERS) and estimated the risk of myocarditis after mRNA-based COVID-19 vaccination based on age, sex, and vaccine type. The main outcomes included crude and expected reporting rates of myocarditis stratified by age and sex. Among 1,626 confirmed cases of myocarditis in a national passive vaccine surveillance program, the crude reporting rates within 7 days after COVID-19 vaccination were higher than expected rates across multiple age and sex strata. The rates of myocarditis cases were highest after the second vaccination dose in adolescent males and in young men. This slightly increased risk should be considered in the context of the benefits of COVID-19 vaccination. A limitation of this study was that clinical outcome and demographic data on patients with myocarditis were limited to what is reported to the CDC and thus, may be incomplete and should not be interpreted within the general population.
Relevant Reading: Patients with acute myocarditis following mRNA COVID-19 vaccination
In-Depth [descriptive study]: This descriptive study of reports of myocarditis to VAERS included 192,405,448 individuals who received a total of 354,100,845 mRNA-based COVID-19 vaccines (BNT162b2 [Pfizer-BioNTech] or mRNA-1273 [Moderna]) between December 2020 and August 2021 in the US. In total, there were 1,626 confirmed cases of myocarditis (median age [IQR], 21 [16-31] years; 82% male; median time to symptom onset [IQR], 2 [1-3] days), where the crude reporting rates within 7 days after COVID-19 vaccination exceeded the expected rates of myocarditis across multiple age and sex strata. The rates of myocarditis were highest after the second dose of the vaccine in adolescent males aged 12 to 15 years (70.7 per million doses of the BNT162b2 vaccine), in adolescent males aged 16 to 17 years (105.9 per million doses of the BNT162b2 vaccine), and in young men aged 18 to 24 years (52.4 and 56.3 per million doses of the BNT162b2 vaccine and the mRNA-1273 vaccine, respectively). Overall, 826 cases of myocarditis occurred in younger individuals under 30 years old, where 98% (792/809) had elevated troponin levels, 72% (569/794) had abnormal electrocardiogram results, and 72% (223/312) had abnormal cardiac magnetic resonance imaging results. Approximately 96% (784/813) of patients were hospitalized, where 87% (577/661) had resolution of symptoms by discharge.
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