By analyzing a cohort of adolescents that developed myocarditis or pericarditis after vaccination against SARS-CoV-2 vaccination, researchers from Yale University School of Medicine were able to pinpoint the underlying mechanism as an overly active innate immune response to the vaccine that led to broad activation of T cells and natural killer (NK) cells. Myocarditis “has been seen in other vaccine contexts, though is most common after viral infection,” Carrie Lucas told reporters at a press conference announcing the findings.