We measured their serum anti-COVID-19 neutralizing antibody levels at 157 ± 42 days after the first vaccination before they received a third dose. They all received the first dose of an mRNA-based vaccine against COVID-19 (0.3 mL Comirnaty ® BioNTech and Pfizer) between 23 April and 30 July 2021, followed by a second dose of the same vaccine 3–4 weeks later. This retrospective observational study involved 76 elderly Japanese patients (median age: 83.5 years interquartile range: 79.8–88.5 years) with cardiovascular disorders ( Table 1). Reduced booster doses could facilitate the worldwide distribution of messenger RNA vaccines. When the third dose was reduced (0.1 mL), changes in 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.

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 brain natriuretic peptide levels. The present retrospective study of 76 patients revealed 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. We recently reported that sub-acute myocarditis occurred following the initial two doses of messenger RNA-based vaccination against coronavirus disease 2019 (0.3 mL Comirnaty ®) in elderly Japanese patients with cardiac dysfunction.

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