On Thursday, the U.S. Centers for Disease Control and Prevention (CDC) said some cases of heart inflammation have been reported after the COVID-19 vaccination, especially among young men who received their second dose of an mRNA vaccine, according to NBC News.

During a presentation to an advisory group of the FDA, Dr. Tom Shimabukuro said 226 cases of myocarditis or pericarditis after COVID vaccination have been confirmed in people younger than age 30. However, further investigation is needed to confirm whether the vaccine was the main cause of concern.

People in their early 20s have been accounted for more than half of the myocarditis cases after vaccination, according to the CDC.

“We clearly have an imbalance there,” said Dr. Shimabukuro, who is the deputy director of the CDC’s Immunization Safety Office.

Most of those cases were sent home after a hospital visit as of the end of May. And it is unclear how many patients were hospitalized and how many were discharged after an ER visit.

Overall, 15 patients remain hospitalized, with three in intensive care units, according to the news outlet. Two of the patients in the ICU had other health problems.

The CDC said it had information on the recovery of 220 patients (80% of these cases) who got better on their own.

Dr. Cody Meissner, a professor in the Department of Pediatrics at Tufts University School of Medicine, said, “It is hard to deny that there’s some event that seems to be occurring in terms of myocarditis.”

Myocarditis is an inflammation of the heart muscle (myocardium), according to Mayo Clinic. By affecting heart muscle and the heart’s electrical system, the condition reduces the heart’s ability to pump and causes rapid or abnormal heart rhythms.

Chest pain, arrhythmia, shortness of breath, fluid retention with swelling of your legs, ankles, or feet, and fatigue are the symptoms of myocarditis. Other symptoms may include a headache, body pain, joint pain, fever, a sore throat, or diarrhea

In many cases, myocarditis improves on its own or with treatment, leading to a complete recovery, say Mayo Clinic.

Vaccine researchers have been looking for a range of potential side effects associated with new COVID vaccines. Dr. Shimabukuro said no major red flags have been reported so far despite the increased number of reported myocarditis cases in young people.

The CDC said it will hold a meeting of its Advisory Committee on Immunization Practices next week to further investigate the evidence and assess the risk of myocarditis after vaccination.

Meanwhile, public health officials have been recommending COVID-19 vaccination for everyone who is 12 and above.

The article appeared on NBC News.