May 24, 2021 -- The CDC is monitoring rare reports of myocarditis, or heart inflammation, among young people after COVID-19 vaccination. So far, there have been “relatively few” cases of myocarditis, according to the latest report by the Advisory Committee on Immunization Practices’ COVID-19 vaccine safety work group.

The few cases of post-vaccination heart inflammation have happened in adolescents and young adults and seem to be more common in males than females. The cases occur more often after a second dose of the Pfizer and Moderna vaccines, and the inflammation typically appears within 4 days after vaccination.

“Most cases appear to be mild, and follow-up of cases is ongoing,” the group wrote.

The vaccine safety work group has reviewed COVID-19 vaccine safety data weekly since the U.S. vaccination program began and has released several updates this year. In the May 17 report, the group discussed the small number of cases of myocarditis, which is an inflammation of the heart muscle that can follow some infections.

The review of the cases in in the early stages, according to The New York Times. The CDC hasn’t yet determined whether a COVID-19 vaccine could cause the heart condition. In the report, the vaccine safety work group said the low rates of myocarditis fall under CDC safety monitoring guidelines and baseline rates in the overall population. Each year, about 10 to 20 of every 100,000 people get myocarditis, the newspaper reported.

“It may simply be a coincidence that some people are developing myocarditis after vaccination,” Celine Gounder, MD, an infectious diseases specialist at Bellevue Hospital Center in New York City, told the newspaper.

“It’s more likely for something like that to happen by chance, because so many people are getting vaccinated right now,” she said.

But members of the vaccine safety work group felt that the information should be shared with doctors and health care providers, they wrote. Specialists in infectious diseases, cardiology, and rheumatology should work together to provide guidance on the diagnosis, treatment, and management of heart inflammation in these rare cases, they said. The work group encouraged doctors to pay attention to any unusual heart symptoms in adolescents and young adults who recently got a vaccine.

“We look forward to seeing more data about these cases so we can better understand if they are related to the vaccine or if they are coincidental,” Yvonne Maldonado, MD, chair of the American Academy of Pediatrics Committee on Infectious Diseases, told the newspaper.

“Meanwhile, it’s important for pediatricians and other clinicians to report any health concerns that arise after vaccination,” she said.

Show Sources


CDC: “COVID-19 VaST Work Group Technical Report -- May 17, 2021.”

The New York Times: “CDC Is Investigating a Heart Problem in a Few Young Vaccine Recipients.”

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