The cardiomyositis that is a rare adverse effect of mRNA-based COVID vaccines is due to immune cell activity as a result of increased levels of the chemokines CXCL10 and interferon-γ (IFN-γ). Blocking CXCL10 and IFN-γ could prevent muscle cell damage in cell culture, and cardiomyositis in animal models. The findings, reported in the Dec. 10, 2025, issue of Science Translational Medicine, suggest a way of mitigating the risk of cardiomyositis.