(339) Eighteen-month follow-up cohort study of post-vaccination COVID-19 myocarditis in France compared with other forms of myocarditis

Background: Although post-COVID-19 mRNA vaccination myocarditis patients appear to have a good prognosis near hospital discharge, their longer-term prognosis and management remain unknown.

Methods: All Individuals aged 12-49 years hospitalized for myocarditis in France between 12/27/2020 and 06/30/2022 were identified and categorized as post-vaccine myocarditis (within 7 days after COVID-19 mRNA vaccine), post-COVID-19 myocarditis (within 30 days of SARS-CoV-2 infection), or conventional myocarditis. We described the occurrence of clinical outcomes (hospital readmission for myopericarditis, other cardiovascular events, all-cause death, and a composite outcome of these events) over the 18 months following hospital admission using weighted Cox models to standardize the comparisons with the conventional myocarditis group. We also longitudinally assessed their medical management after hospital discharge using generalized estimated equation models.

FINDINGS: In total, 4,635 individuals were hospitalized for myocarditis: 558 with post-vaccine myocarditis, 298 post-COVID-19 myocarditis, and 3,779 conventional myocarditis. Patients with post-vaccine myocarditis were younger than those with post-COVID-19 and conventional myocarditis (mean age [standard deviation]: 25.9[8.6], 31.0[10.9], and 28.3[9.4]) and were more frequently men (84%, 67%, and 79%). Post-vaccine myocarditis patients had a lower standardized incidence of the composite clinical outcome than those with conventional myocarditis (32/558 vs 497/3,779 events respectively, weighted Hazard Ratio [wHR], 0.55 [95%CI 0.36-0.85]), whereas cases of post-COVID-19 myocarditis had similar figures (36/298 events, wHR 1.04 [95%CI 0.70-1.55]). The standardized frequency of medical procedures and drugs in patients with post-vaccine myocarditis or post-COVID-19 myocarditis followed a similar trend in the 18 months following hospital discharge to that of patients with conventional myocarditis.

INTERPRETATION: Post-COVID-19 mRNA vaccination myocarditis patients show less frequency of cardiovascular complications than those with myocarditis of other origins at 18 months. However, affected patients, mainly healthy young men, may as well require medical management up to several months after hospital discharge.