CDC says that coronary heart irritation in 16- to 24-year-olds is larger than anticipated after the second injection

A young man in West Virginia receives the vaccine while overlooking the West Virginia Capitol Building at Riggleman Hall.

Stephen Zenner | LightRakete | Getty Images

There have been a higher than expected number of cases of heart inflammation in 16- to 24-year-olds after receiving their second dose of Covid-19 vaccine from Pfizer or Moderna, the Centers for Disease Control and Prevention shared on Thursday Relying on preliminary data from its vaccine safety monitoring system.

The CDC has received reports of 275 cases in this age group as of May 31, the agency said in a presentation prepared for a meeting of the Food and Drug Administration advisory panel on Thursday. Scientists expected between 10 and 102 cases of myocarditis, or pericarditis – in which the heart muscle or the lining of the heart becomes inflamed, according to the CDC.

“We clearly have an imbalance,” said Dr. Tom Shimabukuro of the CDC’s Immunization Safety Office on Thursday on the FDA Advisory Committee on Vaccines and Related Biological Products to discuss safety issues related to the use of Covid-19 vaccines in children 6 months and older.

Although rare, a total of 475 cases of myocarditis or pericarditis have been reported in people aged 30 years and younger, according to the CDC. Most of the patients hospitalized, or 81% of them, had fully recovered from their symptoms, the agency said. May there are still 15 people in the hospital, three of them in the intensive care unit.

The majority of cases appear to occur in men, and the median time to onset of symptoms is two to three days, according to the CDC.

Some of the reported cases could be something other than myocarditis or pericarditis upon further investigation, Shimabukuro said.

The CDC’s Vaccine Safety Group announced last month that it is examining heart infections in “relatively few” people who have received Covid vaccinations.

The cases mostly affected adolescents and young adults and usually occurred within four days of the vaccination, the CDC said at the time. The condition has been seen more often in men and most cases appear to be mild, the agency said, although officials are following up on patients.

The CDC is coordinating its investigation with the FDA, which last month approved the Pfizer BioNTech vaccine for adolescents ages 12-15.

“We still don’t know if this is really related to the vaccine,” said Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, during a virtual question-and-answer event on May 27th. He added that the “handful” of reported cases were “very mild, lasting a day or two,” and usually occurred after a second dose.

Health experts say finding rare side effects once a vaccine or drug is administered to the general population, and if myocarditis is found to be related to the Covid vaccine, the risk is negligible compared to the risks of infection with Covid-19.