Myocarditis, which is inflammation of the heart, occurs in about one in 140,000 people who receive the first dose of the vaccine and one in 32,000 after the second dose, according to a Stanford press release. Among males 30 and younger, that rises to one in 16,750.
Symptoms of the condition include chest pain, shortness of breath, fever and palpitations, which can occur just one to three days after vaccination. Another marker is heightened levels of cardiac troponin, which indicates that the heart muscle has been damaged.
They found that those with myocarditis had two proteins in their blood, CXCL10 and IFN-gamma, which are released by immune cells. Those proteins then activate more inflammation.
"We think these two are the major drivers of myocarditis," said Wu. "Your body needs these cytokines to ward off viruses. It's essential to immune response, but can become toxic in large amounts."
"One of the most striking findings was how much we could reduce heart damage in our models by specifically blocking these two cytokines, without shutting down the entire (desired) immune response to the vaccine," Wu told Fox News Digital, noting that a targeted, "fine‑tuning" immune approach might be enough to protect the heart.
"This points to a possible future way to prevent or treat myocarditis in people who are at the highest risk, while keeping the benefits of vaccination," he added.
The findings were published in the journal Science Translational Medicine.
"This is a very complex study," Fox News senior medical analyst Dr. Marc Siegel told Fox News Digital. "Myocarditis is very rare, and the immune mechanism makes sense."
"Myocarditis is worse with COVID — much more common, and generally much more severe."
Wu agreed, adding that COVID infection is about 10 times more likely to cause myocarditis compared to mRNA-based vaccines.
The researchers emphasized that COVID-19 vaccines have been "heavily scrutinized" for safety and have been shown to have an "excellent safety record."
In rare cases, however, severe heart inflammation can lead to hospitalizations, critical illness or death.
"mRNA vaccines remain a crucial tool against COVID‑19, and this research helps explain a rare side effect and suggests ways to make future vaccines even safer, rather than a reason to avoid vaccination," Wu said.
"The overall benefits of COVID‑19 vaccination still clearly outweigh the small risk of myocarditis for nearly all groups."
