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The Centers for Disease Control and Prevention says 323 cases of heart inflammation have been verified in people who received the Pfizer or Moderna COVID-19 vaccine.
The cases of myocarditis and pericarditis have been seen mostly in teens and young adults between 12 and 39 years old — mostly after the second vaccine dose. Symptoms include chest pain or pressure and abnormal electrocardiogram and blood test results.
The CDC says most people who have experienced this side effect have recovered from symptoms and are doing well. Of the 323 cases, 295 were discharged from the hospital, nine remained hospitalized as of last week and 14 were not hospitalized at all. Outcome data was missing for five of the cases. No deaths have been associated with this side effect.
The CDC says there have been some cases of heart inflammation reported after the Johnson & Johnson vaccine to the Vaccine Adverse Events Reporting System, though not as many as with the Moderna and Pfizer vaccines.
The number of cases has not risen much from last week when CDC Director Rochelle Walensky told reporters at a White House briefing that the agency knew of “over 300” cases.
Officials say the side effect is extremely rare
The CDC says the findings do not change the basic recommendation that all people 12 and older should receive either the Pfizer or Moderna vaccine. However, if a person develops myocarditis after the first dose, a second dose should be delayed until the condition has fully resolved and the heart has returned to a normal state.
“The facts are clear: this is an extremely rare side effect, and only an exceedingly small number of people will experience it after vaccination,” officials said in a statement. “Importantly, for the young people who do, most cases are mild, and individuals recover often on their own or with minimal treatment. In addition, we know that myocarditis and pericarditis are much more common if you get COVID-19, and the risks to the heart from COVID-19 infection can be more severe.”
A representative from the Food and Drug Administration attending the meeting, Dr. Doran Fink, said the agency would add a warning to vaccine fact sheets reflecting the risk of this rare complication.
Naturally occurring heart inflammation is rare, but it does occur from time to time in teens and young adults. The rate seen after these vaccines is slightly higher than would be expected for these ages, prompting concern.
The data is being presented at a meeting of expert advisers convened by the CDC, being held virtually Wednesday and open to the public.
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Officials are also looking at booster shots
The group is also looking at the issue of booster doses. A report from the CDC presented to the expert panel says that the agency would recommend a booster dose only after seeing evidence that people who’ve gotten the vaccines have started getting infected in significant numbers. The agency would not rely solely on a decline in antibodies.
The Advisory Committee on Immunization Practices issues recommendations for the use and scheduling of all approved and authorized vaccines in the United States. It was not scheduled to vote on any recommendations Wednesday regarding the use of the Pfizer or Moderna vaccines.