Cause of very rare Covid vaccine side effect, myocarditis, identified

While extensive studies have found Covid-19 vaccines to be safe, effective, and to have saved millions of lives during the pandemic, these shots come with a rare but real risk of inflamed heart muscle, or myocarditis. Scientists on Wednesday reported that they have identified a pair of immune signals they believe drive these cases — and offered early evidence that these signals can be blocked.

Researchers sifted through previous Covid vaccine studies and identified a pair of immune signaling molecules, or cytokines, present at higher levels in the blood of vaccine recipients with myocarditis: CXCL10 and interferon-gamma (IFN-γ). The authors found that these signals could also be triggered in the lab when immune cells were exposed to the Pfizer and Moderna Covid vaccines, or when mice