FDA expands COVID vaccine warning about possible side effect

The Food and Drug Administration is telling Pfizer and Moderna to expand the warning labels on their COVID-19 vaccines about the risk of a possible heart injury side effect linked to the mRNA shots, primarily in teen boys and young men, citing findings from a study published last year and new agency data.

Orders to expand the warnings were posted Wednesday by the FDA, in letters dated April 17 to Pfizer and BioNTech about their Comirnaty vaccine and Moderna about its Spikevax vaccine.

Both vaccines previously carried warnings about how the risk of the heart side effects — which doctors call myocarditis (an inflammation of the heart muscle) and pericarditis (inflammation of the membrane surrounding the heart) — looked to be higher in young men, generally within the first week after vaccination. While the earlier labels specified ages 18 to 24 years old for Moderna's vaccine and 12 to 17 years old for Pfizer's, the new warning will apply to males ages 16 to 25 for both vaccines.

"Following administration of the 2023-2024 Formula of mRNA COVID-19 vaccines, the highest estimated incidence of myocarditis and/or pericarditis was in males 16 through 25 years of age," the FDA says in the new blanket warning it will require for both vaccines.

The rate of myocarditis and pericarditis was around 8 cases per million doses for children and adults under 65 years old after use of that season's vaccines, the FDA says.

The new warnings ordered by the FDA add that the "highest estimated incidence was in males 16 through 25 years of age," with a rate of 38 cases per million.

The Centers for Disease Control and Prevention has previously described rates of myocarditis and pericarditis as rare after COVID-19 vaccination.

CDC officials told the agency's vaccine advisers last month that acute myocarditis "tends to resolve quickly" after vaccination, and no increased risk had been seen in data from recent seasons in people 12 to 39 years old.

It is unclear whether Pfizer or Moderna disputed the order. They had "within 30 calendar days of the date of this letter" to try to rebut the demand. Spokespeople for Moderna and Pfizer did not immediately respond to a request for comment.

"Americans deserve radical transparency around the safety and efficacy of COVID vaccines and the FDA is delivering on their promise to do just that. Spikevax and Comirnaty should take steps to ensure that individuals are aware of COVID vaccine-related adverse events resulting in myocarditis and pericarditis," Andrew Nixon, a spokesperson for the Department of Health and Human Services, told CBS News in an email. Nixon did not explain why the letters were posted more than a month after they were written.

They appeared on the FDA's website hours ahead of a hearing organized by the Republican-led Senate Homeland Security and Governmental Affairs Committee on "how health officials downplayed and hid myocarditis and other adverse events associated with the COVID-19 vaccines."

Aaron Siri, an attorney who worked closely with Health and Human Services Secretary Robert F. Kennedy Jr. in the past to call on the FDA to pull COVID-19 and other vaccines and vet nominees during the transition, is among the witnesses.

The FDA says the warnings were spurred by new data from the agency's safety surveillance system and results published in October from scientists following up with people who developed COVID-19 vaccine-associated myocarditis.

Talks about this kind of safety labeling change began before the ouster of the FDA's previous top vaccines official, Dr. Peter Marks, multiple people familiar with the situation said, but had not yet been finalized as officials wrestled with how to accurately present the findings. Marks left the FDA on April 5.

Scientists in that study followed up with people who had faced chest pain and elevated amounts of troponin in their blood, a protein that usually signals some kind of heart damage. They were predominantly young adolescent males.

"While their clinical course was nearly always mild with a low prevalence and extent of cardiac dysfunction, myocardial injury was common," the scientists wrote in the study, which was co-authored by FDA officials.

Similar to what the study described, the FDA's new warning also says that the heart MRI findings showed "improvement over time in most people."

"It is not known if these heart MRI findings might predict long-term heart effects of myocarditis. Studies are underway to find out if there are long-term heart effects in people who have had myocarditis after receiving an mRNA COVID-19 vaccine," the FDA said.

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• COVID-19 Vaccine
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• Food and Drug Administration
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