The CDC Says This Delayed Vaccine Side Effect Is Showing Up More Often Now

The agency says it's mainly hitting one age group in particular.

Waking up tired with a headache, stomachache, or even the chills the day after you get vaccinated is nothing out of the ordinary. The Centers for Disease Control and Prevention (CDC) has long been alerting us about the possibility of side effects after the COVID vaccination, which are the result of our bodies building immunity and protection against the novel coronavirus. However, some more concerning, albeit less common, side effects have emerged as an increasing number of people are getting vaccinated, like allergic reactions or blood clots. And now, the CDC says another delayed side effect is showing up more often—especially as younger people are getting vaccinated.

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According to the CDC, the number of heart inflammation cases in young adults after receiving their second mRNA COVID shot from Pfizer or Moderna has been higher than expected. There have been 275 cases of heart inflammation—also known as myocarditis or pericarditis—in young adults ages 16 to 24 years old as of May 31, the CDC said during a presentation for the U.S. Food and Drug Administration (FDA) on June 10. While not that common relative to the 20 million people in that age group who've been vaccinated, the numbers are still much higher than the 10 to 102 cases of heart inflammation the CDC had estimated for that demographic.

"We clearly have an imbalance there," Tom Shimabukuro, MD, the deputy director of the CDC's Immunization Safety Office, said during the meeting, as reported by Reuters.

According to the CDC, myocarditis is inflammation of the heart muscle and pericarditis is inflammation of the outer lining of the heart. The body's immune system can cause the inflammation in response to an infection or some other trigger, like the vaccine. The reaction usually occurs "within several days after COVID-19 vaccination," but not immediately after like an allergic reaction, the CDC says.

More than half of the reported cases of heart inflammation after the COVID vaccine have been in the 16 to 24 age group. Currently, the vaccine is authorized for those as young as 12. As of right now, most of the post-vaccination myocarditis and pericarditis cases have been reported in male adolescents, more often after the second dose than after the first.

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However, this delayed reaction is still rare. Out of more than 141 million fully vaccinated individuals, there have been a total of 789 reported cases of myocarditis or pericarditis as of May 31, per the CDC. For Pfizer, 116 cases were reported after the first dose and 372 were reported after the second. And for Moderna, 100 cases were reported after the first dose and 201 were reported after the second.

The recovery rate for those experiencing myocarditis or pericarditis after vaccination is good as well. Out of 475 reported cases of myocarditis or pericarditis in individuals 30 years or younger, 81 percent fully recovered. Only 15 people remain hospitalized, with three in intensive care as of May 31, the CDC reports.

So due to its uncommonness and successful recovery rate, the CDC still recommends that everyone 12 years and older get vaccinated against COVID. "The known and potential benefits of COVID-19 vaccination outweigh the known and potential risks, including the possible risk of myocarditis or pericarditis," the CDC states on its website. "Also, most patients with myocarditis and pericarditis who received care responded well to medicine and rest and quickly felt better."

The CDC says you should be on the lookout for any of these symptoms of myocarditis and pericarditis after vaccination: chest pain, shortness of breath, and/or feelings of having a fast-beating, fluttering, or pounding heart. If you or your child feel like you are experiencing any of these symptoms within a week after the COVID vaccination, the CDC says you should seek medical care.

RELATED: If You Got This Vaccine, You May Have Low Antibodies Against the India Variant.

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