Scientists explain why mRNA COVID vaccines may rarely cause myocarditis
New research identifies a mechanism for how COVID vaccines may, in rare cases, cause heart inflammation, a condition that may be caused by the disease itself.
Heart inflammation caused by mRNA COVID vaccines is rare.
Yuichiro Chino/Getty Images
COVID vaccines have saved millions of lives from a virus that has killed more than seven million people worldwide. Many safety studies and real-world data from billions of doses show the vaccines are extremely safe and effective. But in rare cases Messenger RNA (mRNA) vaccines have been linked to myocarditis, or inflammation of the heart muscle, which has puzzled scientists and doctors.
Now a new study in mice and cultured human cells may explain why. Researchers Key Immune Response Activity Triggered by mRNA of COVID Vaccines Identified which appears to temporarily damage cardiac tissue at high enough concentrations. The series of experiments described today in Translational Medicine Science, measured damage from two specific cytokines or signaling proteins known to promote inflammation.
This was first reported by doctors in the USA and Israel. COVID-19 vaccine-associated myocarditis in 2021; most cases were observed in teenage boys and men under 30 years of age. A few days after vaccination, victims experienced symptoms including chest pain, shortness of breath, fever and rapid heartbeat.
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The overall risk of vaccine-associated myocarditis is very low, occurring in about one in every 140,000 people who receive the first dose of the vaccine.
There is no specific treatment for myocarditis, although most people can recover within a few months with supportive care, says Mohammad Majeed, an interventional cardiologist at the University of California, Los Angeles.
“We wanted to understand the exact mechanism, because then we can know how to prevent or reverse it,” says Majeed, who was not involved in the new study and treated patients with myocarditis caused by the COVID vaccine. “That’s why I’m excited about this research.”
The immune system generates a barrage cytokines in response to any infection or vaccine. To determine which cytokines play an important role in myocarditis, the study authors first analyzed data from blood samples from two previous studies of people receiving mRNA vaccines. The authors of the new paper focused on two key players that are found in high quantities in people with myocarditis: CXCL10 and interferon gamma. Dousing laboratory human immune cells with mRNA COVID vaccines initiated a noticeable surge in both inflammatory cytokines. The researchers observed a similar cytokine upregulation in vaccinated young male mice.
To confirm the results, the team isolated the vaccine-triggered cytokines in a water bath and injected the liquid directly into mice and lab-created clusters of human heart muscle cells, or “heart spheroids.” Both mouse and human cell clusters showed damage to heart tissue and function, but treatment with cytokine blocking drugs partially restored this function.
The study authors also looked at why vaccine-associated myocarditis is more common in younger men. Researchers have suggested that the sex hormone estrogen may have a protective effect in female animals. They gave genistein, an estrogen-like plant compound that was It has previously been shown to block marijuana-induced inflammation.vaccinated mice and cardiac spheroids, and this markedly prevented tissue damage. “This drug may block the inflammation and cytokine release caused by the COVID vaccine, but it does not reduce the effectiveness of the vaccine,” said Joseph Wu, co-author of the study and director of the Stanford Cardiovascular Institute.
Myocarditis caused by the COVID-19 vaccine remains rare. COVID itself can cause a number of heart problemsincluding irregular heartbeat, heart failure and myocarditis, Majeed says. According to previous studies, people who recovered from COVID experienced approximately There is a 63 percent higher risk of experiencing any heart complications within a year of infection. than people who didn't. Myocarditis caused by COVID is often much more severe than cases caused by the vaccine, Wu said.
“Getting infected with the COVID virus itself has much more serious consequences than getting the COVID vaccine,” he says.
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