mRNA vaccines against SARS-CoV-2 have been widely adopted to combat the COVID-19 pandemic. However, myocarditis has emerged as a rare but severe adverse effect, predominantly affecting young males. Here, we show that mitochondrial vulnerability is associated with mRNA vaccine-associated myocarditis. In our case-control study, patients with postvaccination myocarditis exhibited mitochondrial abnormalities. To examine the impact of mitochondrial damage, mRNA vaccines were administered to Polg+/D257A mice, which heterozygously express a proofreading-deficient mitochondrial DNA polymerase that sensitizes mitochondria to stress. mRNA vaccination in Polg+/D257A mice reduced left ventricular ejection fraction and induced cardiac immune cell infiltration. Bazedoxifene, a selective estrogen receptor modulator, prevented the reduction of cardiac function in Polg+/D257A mice, suggesting a protective role for estrogen signaling. Notably, mRNA vaccination induced mitochondrial reactive oxygen species, resulting in RIPK3 activation, a necroptosis-related kinase, in cardiomyocytes. Collectively, we propose that mitochondrial vulnerability is a potential risk factor for myocarditis following mRNA vaccination, possibly through reactive oxygen species-mediated necroptosis signaling.
© 2026. The Author(s).