Clinical characteristics and prognostic factors of myocarditis associated with the mRNA COVID-19 vaccine.

To analyze the clinical presentation and outcomes of myocarditis after administration of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) messenger RNA (mRNA) vaccine. Nine case series and 15 case reports (74 patients) of myocarditis after administration of the BNT162b2 or mRNA-1273 vaccine were reviewed from PubMed, Scopus, Embase, and Web of Science. We analyzed clinical manifestations, diagnostic findings, and outcomes. In addition, we performed a pooled analysis and investigated risk factors leading to admission to the intensive care unit and recovery with conservative care. Most patients were male (94.6%), and the median age (range) was 17.6 (14-70) years. Patients who received the BNT162b2 (n = 58, 78.4%) vaccine presented fewer systemic symptoms and left ventricular dysfunction than mRNA-1273 recipients. Although patients under 20 years experienced more fever and myalgia, they had better ejection fraction and less prominent myocardial inflammation in magnetic resonance imaging than older patients. The clinical course of all patients was favorable without mortality, and one-third of patients resolved with conservative care alone. Risk factor analyses revealed that patients with gastrointestinal symptoms required intensive care (odds ratio: 20.3, 95% confidence interval 1.90-217, p = 0.013). The risk of fatality in myocarditis subjected to mRNA vaccination seems to be low. However, patients with gastrointestinal symptoms received more intensive care, and a significant proportion of patients recovered with conservative management.