434. Characteristics and long-term outcomes of SARS-CoV-2 associated myocarditis cases in the Military Health System

BACKGROUND: SARS-CoV-2 myocarditis is a complication of COVID-19 and it is important to clarify the risk, clinical characteristics, and long-term outcomes of this complication. It is uncertain whether subsequent SARS-CoV-2 reinfections or COVID-19 vaccine administration after COVID-19-associated myocarditis can trigger a recurrence of myocarditis. METHODS: We examined 5265 Military Health System (MHS) beneficiaries who tested positive for SARS-CoV-2 and enrolled into the Epidemiology, Immunology and Clinical Characteristics of Emerging Infectious Diseases with Pandemic Potential (EPICC) study between March 2020 and April 2022. Possible post-SARS-CoV-2 myocarditis cases were identified using ICD-10 codes, with further medical record adjudication and COVID-19 attribution by a cardiologist using CDC diagnostic criteria. Long-term survival and major myocarditis complications were examined in the medical record. RESULTS: We identified 11 probable post-COVID-19 myocarditis cases, comprising 0.21% (95% CI: 0.10 to 0.37%) of all evaluated SARS-CoV-2 cases. The median age was 28.0 years (IQR = 21.5, 45.8; range = 15.0 to 63.6), and 63.6% were male. Among the myocarditis cases, elevated BMI was common (7/11, 63.6% overweight/obese), and comorbidities were otherwise rare. At the time of initial infection, 10/11 (90.9%) were unvaccinated. There were no deaths by one year post enrollment. Left ventricular dysfunction complicated 3 out of 11 cases (27%), and chronic LV dysfunction developed in one of these cases. One case was complicated by non-sustained polymorphic ventricular tachycardia without further recurrence. Following myocarditis, 8 out of 11 (72.7%) patients received a COVID-19 vaccine; 6 had no documented recurrence of myocarditis post-vaccine. Post-vaccine recurrence was unable to be confirmed in a further two based on the details in the medical record. Three participants had repeat infections after myocarditis with no documented recurrence. CONCLUSION: In MHS beneficiaries, the incidence of post-SARS-CoV-2 myocarditis is low and myocarditis complications were infrequent. We did not confirm myocarditis recurring after reinfection or post-myocarditis vaccination in this case series; this finding requires further study. DISCLOSURES: Simon Pollett, MBBS, AstraZeneca: The IDCRP and the Henry M. Jackson Foundation (HJF) were funded to conduct an unrelated phase III COVID-19 monoclonal antibody immunoprophylaxis trial Mark P. Simons, PhD, AstraZeneca: The IDCRP and HJF were funded to conduct an unrelated phase III COVID-19 monoclonal antibody immunoprophylaxis trial as part of US Govt COVID Response David Tribble, MD, DrPH, AstraZeneca: The IDCRP and HJF were funded to conduct an unrelated phase III COVID-19 monoclonal antibody immunoprophylaxis trial as part of US Govt COVID response Timothy Burgess, MD, MPH, AstraZeneca: The IDCRP and the Henry M. Jackson Foundation (HJF) were funded to conduct an unrelated phase III COVID-19 monoclonal antibody immunoprophylaxis trial