Amelioration of myocarditis after COVID-19 vaccination by low-dose booster

Abstract We recently reported that sub-acute myocarditis occurred following the initial two doses of mRNA-based vaccination against COVID-19 (0.3 mL Comirnaty®) in elderly Japanese patients with cardiac dysfunction. The present retrospective study of 76 patients shows that myocarditis following the initial doses persisted for 12 months, was associated with low levels of neutralizing antibodies, and was ameliorated by reducing the third vaccine dose. Low neutralizing antibody levels (<220 U/mL) after the initial doses were an independent predictor of persistent clinical events, defined as death or marked changes in the brain natriuretic peptide levels. When the third dose was reduced (0.1 mL), changes in the brain natriuretic peptide levels were significantly smaller (P = 0.02, n = 25), no deaths occurred due to heart failure, and neutralizing antibody levels increased 41-fold (P < 0.001) compared with the initial doses. Reduced booster doses could facilitate the worldwide distribution of mRNA vaccines.