Abstract 11847: Acute Myocarditis Following COVID-19 mRNA Vaccination

Introduction: Acute myocarditis after coronavirus disease 2019 (COVID-19) mRNA vaccination is not well described. Recent public reports have signaled that this is an entity that requires ongoing surveillance. The goal of this study is to investigate myocarditis incidence following COVID-19 mRNA vaccination, and to report the clinical course and outcomes. Methods: This is a retrospective population-based cohort study performed at Kaiser Permanente Southern California (KPSC), an integrated health care system in California. Patients who received at least one dose of BNT162b2 (Pfizer) or mRNA-1273 (Moderna) mRNA vaccine were included. Clinically significant cases of acute myocarditis within 10 days of COVID-19 mRNA vaccination were identified between 12/14/2020 and 5/31/2021. Key demographic, clinical, laboratory, diagnostic data, and clinical course were obtained from medical record review. Results: Of 1,776,608 KPSC members who received at least one dose of COVID-19 mRNA vaccines, 12 developed acute myocarditis within 10 days following vaccination, for an estimated incidence of 6.6 cases per 1 million patients. All patients were relatively healthy White or Hispanic men between the ages of 18 and 40 years. Patients reported chest pain two to eight days after vaccine administration (Moderna N=5; Pfizer N=7). Eleven patients developed myocarditis after the second dose, and one after the first dose. Troponin I elevations ranged from 1.53-32.30 ng/mL. All cases were self-limited, with troponin peaking within 24-48 hours of admission and symptom resolution prior to discharge. None of the patients had evidence of decompensated heart failure. Length of stay was 1-4 days, with all patients discharged home and no recurrence, readmission, or major adverse cardiac events. Conclusions: Acute myocarditis after COVID-19 mRNA vaccination is a rare and self-limited event that warrants further description and investigation.