More than 300 cases of heart inflammation after Covid-19 vaccinations have been reported in young people, Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said Thursday.
"The case are rare," she said. "Over 20 million adolescents and young adults [have been] vaccinated in the United States."
Still, the cases of either myocarditis or pericarditis, which involve inflammation of the heart or the surrounding tissue, are higher than what would be expected for this age group.
The CDC's independent advisory group, called the Advisory Committee on Immunization Practices, will meet next week to review the cases. The meeting was originally scheduled for Friday, but was rescheduled late Thursday after President Joe Biden signed a bill into law declaring Juneteenth a federal holiday. Because June 19 falls on a Saturday this year, it will be observed on Friday, June 18.
The group will discuss the latest research and safety data on myocarditis following shots, but is not expected to make any changes to Covid-19 vaccination recommendations. The shot from Pfizer-BioNTech is the only one authorized so far for children ages 12 through 17, though young adults 18 and older can receive either Pfizer, Moderna or Johnson & Johnson's vaccines.
It remains unclear whether the vaccines are the cause of the heart problem, though the CDC has said that evidence for a link is growing stronger.
Dr. Paul Offit, a vaccine researcher at the Children's Hospital of Philadelphia, said the meeting should result in a "clear understanding of the current risks for either children or young adults" from the vaccine.
During the briefing Thursday, Walensky said the CDC has asked "clinicians to be on the lookout for and report patients with symptoms of myocarditis or pericarditis following vaccination."
Symptoms can include fever and fatigue, as well as shortness of breath and chest pain. Most cases have not been serious.
Download the NBC News app for full coverage of the coronavirus outbreak
"The vast majority have fully resolved with rest and supportive care," Walensky said.
Indeed, "people who have had this side effect tend to have had mild or minimal symptoms that resolve within several days," said Dr. Katie Passaretti, medical director for infection prevention at Atrium Health in Charlotte.
Next week's gathering of experts "is yet another demonstration of our ongoing efforts to keep safety central in everything we do," Walensky said. "Getting vaccinated is our way out of this pandemic."