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.
Most people who have experienced this side effect have recovered from symptoms and are doing well, according to data presented Wednesday at a public meeting of the CDC's vaccine advisory committee. 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.
Symptoms include chest pain or pressure and difficulty breathing, says Dr. Kristen Sexson Tejtel, a cardiologist at Texas Children's Hospital who has treated people with the vaccine-related condition. For people experiencing symptoms, "the best thing to do is to talk to their physician or come to the emergency room for evaluation," Tejtel says, where blood tests and heart imaging results can confirm the diagnosis.
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, the CDC recommends that 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."
Health experts agree that the benefits of being protected from COVID-19 outweigh the risks of developing this temporary heart condition from a vaccine. "There's no zero risk proposition," says Dr. Brian Feingold, medical director of the heart transplant program at Children's Hospital of Pittsburgh. "If you're statistically going after what's safest, the data right now stacks up [to show] that vaccines are absolutely the safer route."
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.
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 did not vote on any recommendations Wednesday regarding the use of the Pfizer or Moderna vaccines.
Pien Huang contributed to this report