CDC Investigating Possible Link Between COVID Vaccines and Mild Heart Condition in Young Males

Getty A person getting vaccinated

There is growing evidence of a link between the COVID-19 vaccine and cases of a mild heart condition in young people, primarily men, after receiving their second dose, the Centers for Disease Control said Thursday.

The number of cases is low - the CDC has identified 283 cases of the heart inflammation, called myocarditis, in people under 30 years old - but higher than expected. The CDC typically sees fewer than 100 cases of the condition in this age group.

The CDC said that it needs more research into whether the vaccine was the cause of the myocarditis cases, and advisors will meet next week to discuss a possible link.

RELATED: What Parents Need to Know Now That Kids Aged 12 to 15 Are Eligible for a COVID Vaccine

The federal health agency said that those cases were still "rare" and resolved quickly. "Most patients who received care responded well to medicine and rest and quickly felt better."

Most cases were in men in their teens and early 20s, despite being a smaller proportion of Americans who have received the COVID-19 vaccine.

"We clearly have an imbalance there," Dr. Tom Shimabukuro, deputy director of the CDC's Immunization Safety Office, said in a presentation to a Food and Drug Administration advisory committee on Thursday.

The condition typically occurred within a week after receiving the second dose of Pfizer or Moderna's vaccine, and most patients - 91% - were sent home after going to the hospital. Of the hundreds of cases, 15 are currently hospitalized and three are in intensive care units. Two of the patients in ICUs had other health conditions.

RELATED VIDEO: Vaccinated Americans Can Now Go Without Masks in Most Indoor and Outdoor Places, CDC Says

Myocarditis is an inflammation of the heart that typically occurs after a viral infection, and can affect its ability to pump, causing rapid or irregular rhythms, according to the Mayo Clinic. The symptoms can include chest pain, shortness of breath, fatigue and heart arrhythmias. In severe cases, myocarditis can lead to clotting, which can cause stroke or heart attack.

There may be no link between the vaccines and myocarditis, the CDC said, but it will investigate to ensure the safety of the vaccines, and to determine if physicians should be warned of risks. Contracting COVID-19 carries a far higher risk of heart problems than the vaccine.

"We're still learning about the rates of myocarditis," Shimabukuro said. "As we gather more information, we'll begin to get a better idea of the post-vaccination rates and hopefully be able to get more detailed information by age group."

As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the CDC, WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.