Younger males at greatest risk of myocarditis after mRNA-based COVID-19 vaccination

An analysis of US-based passive surveillance reporting data has found that the risk of myocarditis after vaccination with mRNA-based COVID-19 vaccines is greatest after the second vaccine dose in adolescent males and young men.

The study, published in JAMA, examined myocarditis cases reported to the Vaccine Adverse Event Reporting System (VAERS) occurring after receiving mRNA-based COVID-19 vaccines (tozinameran [BNT162b2; Pfizer-BioNTech] or elasomeran [mRNA-1273; Moderna]) between December 2020 and August 2021. Rates of myocarditis were calculated across age and sex strata and compared with expected rates taken from 2017-2019 claims data.

Overall, 192 405 448 patients aged ≥12 years received 354 100 845 mRNA-based COVID-19 vaccine doses during the study period. There were 1991 reports of myocarditis to VAERS; of these, 1626 met the case definition of myocarditis 1. The median age of cases was 21 years (IQR 16-31 years), the median time to symptom onset was 2 days (IQR 1-3 days), 82% were male and 82% occurred after the second vaccine dose. There were no confirmed myocarditis-related deaths in patients under 30 years of age after vaccination. Reporting rates for myocarditis within 7 days after vaccination exceeded expected rates of myocarditis across multiple age and sex strata, with rates of myocarditis greatest after the second dose in males aged 12 to 15 years (70.7 per million doses of tozinameran), in males aged 16 to 17 years (105.9 per million doses of tozinameran), and in men aged 18 to 24 years (52.4 and 56.3 per million doses of tozinameran and elasomeran, respectively). Symptoms most commonly reported in verified cases of myocarditis in patients <30 years of age included chest pain, pressure, or discomfort (89%) and dyspnoea or shortness of breath (30%); 98% had elevated troponin levels. Most cases (87%) were treated with non-steroidal anti-inflammatories; intensive therapies were rare (14 cases), and no cases required heart transplant, extracorporeal membrane oxygenation, or a ventricular assist device. The researchers note that "major presenting symptoms appeared to resolve faster in cases of myocarditis after COVID-19 vaccination than in typical viral cases of myocarditis."