The COVID-19 vaccine is likely linked with rare cases of heart inflammation in U.S. teens and young adults — particularly in males. But the benefits of the vaccine still outweigh the risks for every age group at this time, according to data presented Wednesday (June 23) at a meeting of the Centers for Disease Control and Prevention (CDC).
As of June 11, the CDC's vaccine adverse event reporting system logged 323 confirmed U.S. cases of heart muscle inflammation, or myocarditis, shortly after receipt of COVID-19 mRNA vaccines in people ages 12 to 29, Dr. Tom Shimabukuro, deputy director of the CDC's Immunization Safety Office, said during the meeting. In most of these cases, recipients experienced chest pain and shortness of breath within four days of the second COVID-19 shot. Most of these people were hospitalized. But the vast majority were discharged within a few days from the hospital and had recovered from their symptoms by that time.
And overall, this side effect appears rare — data so far show the rate of myocarditis following COVID-19 vaccine in people ages 12 to 39 is 12.6 cases per 1 million people vaccinated. Still, for young males, the rate is higher, up to 66 cases per 1 million people, Shimabukuro said, which is much higher than the background rate of myocarditis cases that would be expected in the short period of time after vaccination for this age group.
"Data available to date suggest a likely association of myocarditis with mRNA vaccination in adolescents and young adults," Dr. Grace M. Lee, chair of the COVID-19 Vaccine Safety Technical Subgroup of the CDC's Advisory Committee on Immunization Practices (ACIP), said during the meeting.
Still, the data showed a clear benefit of the vaccine compared with the risk of myocarditis for all age groups.
The CDC said that for every million teen males who are vaccinated, an estimated 5,700 cases of COVID-19 and 215 hospitalizations would be prevented; an estimated 56 to 69 cases of myocarditis would be expected.
"Currently, the benefits still clearly outweigh the risks for COVID-19 vaccination in adolescents and young adults," Dr. Sara Oliver, an epidemic intelligence service officer at the CDC, said during the meeting.
Experts from a CDC advisory panel on vaccinations seemed to largely agree with this interpretation.
"I clearly think the presentation you've given today shows the benefit-risk balance in favor of benefit," Dr. José Romero, ACIP chair and Arkansas' Secretary of Health, said during the meeting.
But experts stressed the need for further follow-up of these patients to evaluate the potential long-term risks of myocarditis, and to figure out how to handle cases of myocarditis that happen after the first dose.
Preliminary recommendations from the CDC, which may be updated before they are finalized, say that people who experience myocarditis after the first dose should defer their second dose until more information is known, Oliver said. But even these patients might still consider receiving their second shot after they've recovered from their myocarditis symptoms under certain circumstances, Oliver said. (These circumstances were not specified at the 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," according to a statement co-signed by more than a dozen organizations following the meeting, including the U.S. Department of Health and Human Services, CDC, American Academy of Pediatrics and American Heart Association. "Importantly, for the young people who do, most cases are mild, and individuals recover often on their own or with minimal treatment," the statement said.
The CDC still recommends COVID-19 vaccination for everyone ages 12 and older.
Originally published on Live Science.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.