Hypersensitivity Lymphohistiocytic Myocarditis After Moderna mRNA-1273 Vaccine

In the important report by Chow and Lai,1 a healthy 45-year-old woman started to feel unwell, citing fatigue, palpitations, and dyspnea 1 week after her first Moderna mRNA-1273 vaccine dose. One month after her second dose, she lost consciousness for 5 minutes, with frothing at the mouth, tonic-clonic movements, and urinary incontinence. Two weeks later, Holter monitoring showed multiple runs of sustained ventricular tachycardia. Magnetic resonance imaging scans showed subepicardial delayed gadolinium enhancement compatible with myocarditis. Coronary angiography revealed 50% occlusive plaque of the posterior descending artery and 90% stenosis of 1 of 2 right posterolateral artery branches. Endomyocardial biopsy revealed lymphohistiocytic infiltrates with scattered eosinophils and focal myocyte injury suggesting postvaccination hypersensitivity myocarditis. This report raises important issues concerning the type, delayed appearance, and causality of myocarditis as well as measures to avoid such events. Myocarditis is an inflammatory disease that affects the myocardium and the...