Younger persons accounted for more than half of those with a heart issue after vaccination.

More young adults than expected have reported heart inflammation following Covid-19 vaccination The condition, called myocarditis, is usually mild, but a handful of patients remain hospitalized. NBC News

A higher-than-usual number of cases of a type of heart inflammation has been reported following Covid-19 vaccination, especially among young men following their second dose of an mRNA vaccine, the Centers for Disease Control and Prevention said Thursday.

Overall, 226 cases of myocarditis or pericarditis after vaccination in people younger than age 30 have been confirmed, Dr. Tom Shimabukuro, deputy director of the CDC's Immunization Safety Office, said during a presentation to a Food and Drug Administration advisory group.

Further investigation is needed, however, to confirm whether the vaccination was the cause of the heart problem.

Normally, fewer than 100 cases would be expected for this age group.

Teenagers and people in their early 20s accounted for more than half of the myocarditis cases reported to the CDC's safety monitoring systems following Covid-19 vaccination, despite representing a fraction of people who have received the shots.

"We clearly have an imbalance there," Shimabukuro said.

The vast majority of the cases were sent home following a visit to a hospital as of the end of May. It's unclear how many patients were admitted to the hospital, or, for example, were discharged following a visit to the emergency room. Fifteen patients remain hospitalized, with three in intensive care units. Two of the patients in the ICU had other health problems.

The CDC had information on the recovery of patients in 220 cases; in more than 80 percent of these cases, patients got better on their own. ...