Over 800 cases of rare heart problems have been reported following vaccinations with the COVID-19 vaccines made by Pfizer-BioNTech and Moderna, the US Centers for Disease Control and Prevention (CDC) said.

"We clearly have an imbalance there," said Dr. Tom Shimabukuro, deputy director of the CDC's Immunization Safety Office, in a New York Times report.

Based on the data presented, people ages 12 to 24 accounted for more than half of the heart problems cases reported to the CDC's safety monitoring systems following COVID-19 vaccination.

A total of 226 cases of myocarditis or pericarditis after vaccination among people younger than age 30 have also been confirmed.

The report also showed at least 216 people experienced myocarditis or pericarditis after one dose of either Pfizer-BioNTech or Moderna, and 573 after the second dose as of May 31.

It was also found that there was a predominance of males in younger age groups among the reported rare heart inflammation cases.

Myocarditis is a condition that involves inflammation of the heart muscle or myocardium.

The data also revealed most patients or at least 81 percent had full recovery of symptoms while 19 percent still had ongoing signs or symptoms.

In an NBC News report, Dr. Cody Meissner, chief of pediatric infectious diseases at the Tufts Children's Hospital in Boston, added "it is hard to deny that there's some event that seems to be occurring in terms of myocarditis." The CDC, meanwhile, said it will still need to confirm whether the vaccination was the cause of the heart problem.

The agency will hold a meeting of its Advisory Committee on Immunization Practices on June 18 to further discuss the matter and to assess the risk of myocarditis or pericarditis following immunization.