Myocarditis following COVID-19 vaccination in adolescents and adults: a cumulative experience of 2021.

Clinical course and outcomes of myocarditis after COVID-19 vaccination remain variable. We retrospectively collected data on patients > 12 years old from 01/01/2021 to 12/30/2021 who received COVID-19 messenger RNA (mRNA) vaccination and were diagnosed with myocarditis within 60 days of vaccination. Myocarditis cases were based on case definitions by authors. We report on 238 patients of whom most were male (n = 208; 87.1%). The mean age was 27.4 ± 16 (range 12-80) years. Females presented at older ages (41.3 ± 21.5 years) than men 25.7 ± 14 years (p = 0.001). In patients > 20 years of age, the mean duration from vaccination to symptoms was 4.8 days ± 5.5 days, but in < 20, it was 3.0 ± 3.3 days (p = 0.04). Myocarditis occurred most commonly after the Pfizer-BioNTech mRNA vaccine (n = 183; 76.45) and after the second dose (n = 182; 80%). Symptoms started 3.95 ± 4.5 days after vaccination. The commonest symptom was chest pain (n = 221; 93%). Patients were treated with non-steroidal anti-inflammatory drugs (n = 105; 58.3%), colchicine (n = 38; 21.1%), or glucocorticoids (n = 23; 12.7%). About 30% of the patients had left ventricular ejection fraction but more than half recovered the on repeat imaging. Abnormal cardiac MRIs were common; 168 patients (96% of 175 patients that had MRI) had late gadolinium enhancement, while 120 patients (68.5%) had myocardial edema. Heart failure guideline-directed medical therapy use was common (n = 27; 15%). Eleven patients had cardiogenic shock; and 4 patients required mechanical circulatory support. Five patients (1.7%) died; of these, 3 patients had endomyocardial biopsy/autopsy-confirmed myocarditis. Most cases of COVID-19 vaccine myocarditis are mild. Females presented at older ages than men and duration from vaccination to symptoms was longer in patients > 20 years. Cardiogenic shock requiring mechanical circulatory support was seen and mortality was low. Future studies are needed to better evaluate risk factors, and long-term outcomes of COVID-19 mRNA vaccine myocarditis.