evidence: Myocarditis is a rare side effect of mRNA COVID-19 vaccines, which have been used with great success as protection against the SARS CoV-2 virus and its variants. Generally, the condition is highly treatable, but it has caused concern in some quarters about the vaccines’ safety. We spoke with Carrie Lucas, PhD, associate professor of immunobiology at Yale School of Medicine, and Akiko Iwasaki, PhD, Sterling Professor of Immunobiology, about their recent study which uncovers clues to why this complication can occur. [...] Why can the mRNA vaccine affect the heart?