The “one in 35” comes from a observational study conducted by researchers at the University Hospital Basel in Switzerland. It has attracted attention because it actively looked for myocardial injury.

The study enrolled 777 hospital employees who were scheduled to receive a Moderna (mRNA-1273) booster shot. Participants were relatively young (median age, 37 years), and approximately 70% were women. Blood samples were collected immediately before injection and again 48–96 hours afterwards, corresponding to the period during which mRNA-associated myocarditis has most frequently been reported.

Unlike passive surveillance systems that rely on clinically apparent cases, the investigators measured high-sensitivity cardiac troponin T (hs-cTnT) in every participant. Troponin is the most sensitive biomarker of myocardial injury and can detect even minimal cardiac muscle damage that may occur without causing symptoms.

To investigate potential biological mechanisms underlying myocardial injury, the researchers also measured circulating inflammatory cytokines and SARS-CoV-2–specific antibodies.

They found no evidence that participants with myocardial injury exhibited greater systemic inflammatory responses or differed in prior SARS-CoV-2 infection status. However, affected individuals had lower concentrations of interferon-λ1 (IL-29) and granulocyte-macrophage colony-stimulating factor (GM-CSF), prompting the authors to hypothesize that these immune mediators may play protective roles in limiting injection-associated injury.