COVID-19 vaccines + heart inflammation: A timeline of CDC updates

Since April, the CDC has been following reports of people experiencing heart inflammation after receiving Pfizer or Moderna's mRNA vaccines, occurring mostly among adolescent and young adult vaccine recipients. 

Here's a timeline of updates from the CDC since it began receiving reports of myocarditis (heart muscle inflammation) and pericarditis (heart lining inflammation) potentially linked to COVID-19 vaccines: 

April 2021

In April, the CDC started noticing an increase of heart inflammation reports in the U.S., particularly among adolescents and young adult vaccine recipients. 

May 17 

The CDC's Advisory Committee on Immunization Practices said it was reviewing "relatively few" reports of heart inflammation among teenagers and young adults in a May 17 update. At the time, the group did not provide an exact number, but said the number of reports wasn't higher than would be expected among the general population. The cases occurred predominantly in males, were mostly mild and were more common after the second dose of vaccine than the first, the statement said. 

The group said it was unable to determine whether there is a causal relationship between the reports of heart inflammation and the vaccine, calling for further study and follow-up. 

May 28 

The CDC called on physicians to report all cases of heart inflammation after mRNA COVID-19 vaccination to the agency's national Vaccine Adverse Event Reporting System in a May 28 statement

"There has not been a similar reporting pattern observed after receipt of the [Johnson & Johnson] COVID-19 vaccine," the agency noted. "In most cases, patients who presented for medical care have responded well to medications and rest and had prompt improvement of symptoms." 

If younger patients present with acute chest pain, shortness of breath, or palpitations, physicians should consider heart inflammation and ask about COVID-19 vaccination history, the agency said, along with several other clinician recommendations. 

June 10 

The agency's vaccine safety committee said it would hold an emergency meeting to discuss a potential link between heart inflammation and mRNA COVID-19 vaccines during a June 10 presentation to the FDA's advisory panel. At the time, the group said it had received 275 reports of heart inflammation in people ages 16-25 after their second dose of Pfizer or Moderna's vaccine, adding that the number of cases in that age group was higher than the 10 to 102 cases scientists anticipated. 

Among people ages 30 and younger, 475 cases of heart inflammation were reported to the CDC, the group said during the June 10 meeting. 

June 23 

There's a "likely association" between rare heart inflammation and mRNA COVID-19 vaccines among adolescent and young adult recipients, the CDC's Advisory Committee on Immunization Practices said June 23, with officials emphasizing the condition is still rare and encouraging vaccination among everyone who is eligible. 

As of June 11, 1,226 cases of heart inflammation have been reported to the agency's national Vaccine Adverse Event Reporting System, occurring mostly among adolescent and young adult vaccine recipients. Of those, 232 cases occurred among people younger than 29, the group said. 

For Moderna and Pfizer's vaccine combined, there have been 12.6 cases of heart inflammation per million doses, the group said, adding that the CDC is continuing to work with the FDA on the investigation. 

The CDC, HHS, and a number of other U.S. medical groups issued a joint statement emphasizing the benefits outweigh the risk of potential harm after the June 23 meeting. 

"The facts are clear: this is an extremely rare side effect, and only an exceedingly small number of people will experience it after vaccination. 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 from COVID-19 infection can be more severe." 

During the same meeting, a representative from the FDA said it will add a warning statement about the risks and characteristics of the rare condition to Moderna and Pfizer's vaccine fact sheets.


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