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It's been a little more than a month since adolescents as young as 12 became eligible in the United States to receive the Pfizer vaccine against COVID-19, and nearly all reports have been positive: The vaccine is very effective in this age group, and the vast majority of kids experience mild side effects, if any — the same sore arm or mild flulike symptoms seen among adults who get the shot.

The Centers for Disease Control and Prevention has recommended that everyone 12 and older get vaccinated against COVID-19, and the rollout is well underway: According to the CDC, nearly 7 million U.S. teens and preteens (ages 12 through 17) have received at least one dose of a COVID-19 vaccine so far.

Still, soon after the Food and Drug Administration authorized the use of Pfizer's vaccine in young people, federal agencies began receiving 

 of mild chest pain or other signs of possible heart inflammation (known as myocarditis) in a small percentage of recently vaccinated teenagers.

CDC Director Rochelle Walensky said at a White House briefing Thursday that there have been more than 300 cases of heart inflammation reported among the millions of teens and young adults who have received one of the vaccines made by Moderna or Pfizer. She said that in the "vast majority" of cases, the inflammation went away.

An expert advisory committee to the health agency is expected to

So, in the meantime, should parents of teens hesitate to have their kids vaccinated against COVID-19? Vaccine experts and 

the American Academy of Pediatrics say no, don't hesitate

. It's good for doctors and patients to be aware that there might be a connection between the messenger RNA vaccines and heart inflammation, and to report to their pediatrician anything they see in that first week after vaccination. But it is also important, the CDC notes, to recognize that even if this does turn out to be an extremely rare side effect of the vaccine, "most patients who received care responded well to medicine and rest and quickly felt better." And the serious risks of COVID-19 — even for young healthy people — outweigh the risks of any possible side effects from the vaccine. Here are some questions you may have, and what's known:

, and pericarditis, also being investigated, is an inflammation of the sac around the heart.

 thousands of cases of myocarditis were diagnosed

 in the U.S. and around the world each year, often triggered by the body's immune response to infections. SARS-CoV-2, the virus that causes COVID-19, can trigger it, and so can cold viruses, and staph and strep and HIV. Other causes include toxins and allergies.

Symptoms include chest pain and shortness of breath. It's often mild enough to go unnoticed, but a full-blown case in adults can cause arrhythmias and heart failure that require careful treatment with multiple medications, and several months of strict rest. In a case study of seven teenagers who got myocarditis following vaccination 

all seven got better after routine treatment with anti-inflammatory drugs.

 of the Northwestern University Feinberg School of Medicine, a spokesperson for the American Academy of Pediatrics, says vaccine-related myocarditis in teens is not all that worrisome. "Although they appear with some symptoms of chest pain, and maybe some findings on EKGs, all of the cases we've seen have been on the mild end of the spectrum," he says.

Several hundred reports about the inflammation have been filed with the federal government's Vaccine Adverse Event Reporting System, or VAERS; that's a repository of reports sent in by health professionals and patients about any health events they spot in the hours or days after vaccinations. Many of the events reported turn out to be coincidental — not caused by a vaccine. The database is just meant as a starting point for further investigation and not proof of cause and effect. But as NPR's Geoff Brumfiel

, "when millions of people are vaccinated within a short period, the total number of these reported events can look big."

That said, anecdotes reported by doctors in medical journals and reports to VAERS suggest that both of the mRNA vaccines authorized for use in the U.S. — the Pfizer and Moderna vaccines — might slightly increase the incidence of myocarditis in young people. In 2003, a

 estimated the background incidence of myocarditis to be 1.13 cases in 100,000 children per year.

Paul Offit, professor of pediatrics at the Children's Hospital of Philadelphia and a member of an FDA vaccine advisory committee, says there likely is a causal link between the heart inflammation some doctors are seeing in these teens and the second dose of vaccine. "I think it's real," he says, but he hastens to add that the effect is exceedingly small – based on the data collected so far, maybe one in 50,000 vaccinees between the ages of 16 and 39. "And the good news is at least so far it looks to be transient and self-resolving."

Still, maybe I should wait to get my teen vaccinated and see how this plays out?

Uhm, no, according to several vaccine experts contacted by NPR. And this is where a little math comes in handy.

"Take a stadium full of 100,000 people between the ages of 16 and 39, which is the subset that appears to be at greater risk," Offit says. "Vaccinate all of them, and two might get myocarditis." But if you don't vaccinate any of the 100,000, he estimates that about 1,300 would eventually get COVID-19. And those numbers are likely to increase this winter.

About 1 in 1,000 children who get COVID-19 have gone on to develop a condition called

 (multisystem inflammatory syndrome in children), says Offit, and most of those kids have had some level of myocarditis. In addition, the coronavirus has directly caused myocarditis in some children and adults. Which of the two stadiums in Offit's metaphor would have more cases of myocarditis — the vaccinated children or unvaccinated kids — is not known precisely. But Offit says he suspects it would be the unvaccinated group. And there's no doubt that 1,000 unvaccinated children would suffer more illnesses related to COVID-19. "A choice not to get a vaccine is not a choice to avoid myocarditis," he says. "It's a choice to take a different risk — and I would argue a more serious one" — of developing a bad case of COVID-19 or long COVID-19 or myocarditis as a result of COVID-19.

Are the experts advising their own kids in this age group to get vaccinated?

Yes. "I understand people having concerns," 

 says. She's a parent and professor of pediatric infectious diseases at the Oregon Health and Science University as well as the senior author on a

 In the report, Guzman-Cottrill and her colleagues analyzed the cases of seven boys around the country who developed myocarditis within four days of receiving the Pfizer-BioNTech vaccine.

She and her family recently faced the vaccination decision for her 13-year-old daughter — and said a wholehearted yes to the shot.

Guzman-Cottrill suspects there may turn out to be a slightly increased risk of heart inflammation from vaccination in young people, but she and her co-authors note in the 

report that a direct cause-and-effect connection — even in these seven cases — has yet to be established. And she's impressed that despite the millions of doses that have so far been delivered to teens, no clear and serious post-vaccination problems have shown up. "The emergency departments and urgent care clinics are not filled with teenagers complaining of chest pain," she says.

She's treated unvaccinated teens who developed severe myocarditis from an infection with the COVID-19 virus, and others who developed COVID-19 pneumonia and respiratory failure. Seeing those teens struggle — lacking the powerful immune protection the vaccine provides — was enough for her to suggest vaccination to her daughter, who got her second vaccination this week.

"She saw it as a pathway back to a normal, post-pandemic life," Guzman-Cottrill says.

And that's where public health comes in. "We really need a highly vaccinated student body when kids return to the classroom this fall," Guzman-Cottrill says, "so we don't see surges in COVID-19 cases."

Joanne Silberner, a former health policy correspondent for NPR, is a freelance journalist in Seattle.

Health

COVID-19

Joanne Silberner

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Health officials are investigating reports of mostly mild, temporary and treatable heart inflammation that may or may not be causally linked to vaccination with an mRNA vaccine against COVID-19.

Pfizer's COVID vaccine in teens and myocarditis: What you need to know

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