Major study reveals why COVID vaccine can trigger heart issues, especially in one group

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.

"It's not a heart attack in the traditional sense," Wu told Fox News Digital. "There's no blockage of blood vessels as found in most common heart attacks. When symptoms are mild and the inflammation hasn't caused structural damage to the heart, we just observe these patients to make sure they recover."

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.

In mouse and heart tissue models, high levels of these proteins led to signs of heart irritation, similar to mild myocarditis.

"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 team also found that genistein, an estrogen-like natural compound found in soybeans, reduced inflammation in lab tests, but this has not yet been tested in humans.

The findings were published in the journal Science Translational Medicine.

"Myocarditis is worse with COVID - much more common, and generally much more severe." 

"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."

"These findings do not change what people should do right now, because our work is still at the preclinical (mouse and human cells) stage," he said. "Clinical studies will be needed to confirm whether targeted treatments are safe and effective."

The researcher also added that myocarditis risk could rise with other types of vaccines.

The study was funded by the National Institutes of Health and the Gootter-Jensen Foundation.