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There is growing evidence of a link between the COVID-19 vaccine and cases of a mild heart condition in young people, primarily men, after receiving their second dose, the Centers for Disease Control said Thursday.
The number of cases is low - the CDC has identified 283 cases of the heart inflammation, called myocarditis, in people under 30 years old - but higher than expected. The CDC typically sees fewer than 100 cases of the condition in this age group.
The CDC said that it needs more research into whether the vaccine was the cause of the myocarditis cases, and advisors will meet next week to discuss a possible link.
The federal health agency said that those cases were still "rare" and resolved quickly. "Most patients who received care responded well to medicine and rest and quickly felt better."
Most cases were in men in their teens and early 20s, despite being a smaller proportion of Americans who have received the COVID-19 vaccine.
"We clearly have an imbalance there," Dr. Tom Shimabukuro, deputy director of the CDC's Immunization Safety Office, said in a presentation to a Food and Drug Administration advisory committee on Thursday.
The condition typically occurred within a week after receiving the second dose of Pfizer or Moderna's vaccine, and most patients - 91% - were sent home after going to the hospital. Of the hundreds of cases, 15 are currently hospitalized and three are in intensive care units. Two of the patients in ICUs had other health conditions.
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Myocarditis is an inflammation of the heart that typically occurs after a viral infection, and can affect its ability to pump, causing rapid or irregular rhythms, according to the Mayo Clinic. The symptoms can include chest pain, shortness of breath, fatigue and heart arrhythmias. In severe cases, myocarditis can lead to clotting, which can cause stroke or heart attack.
There may be no link between the vaccines and myocarditis, the CDC said, but it will investigate to ensure the safety of the vaccines, and to determine if physicians should be warned of risks. Contracting COVID-19 carries a far higher risk of heart problems than the vaccine.
"We're still learning about the rates of myocarditis," Shimabukuro said. "As we gather more information, we'll begin to get a better idea of the post-vaccination rates and hopefully be able to get more detailed information by age group."
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