Now that the Pfizer-BioNTech COVID-19 vaccine has been approved for use in children ages 5 through 11, there’s concern that some will develop myocarditis, a swelling of the heart muscle.
But it’s not clear how many – and millions of children will have to be vaccinated before it is known.
Trials in younger children have been too small to show the rare side effect, just as trials in adults did not reveal myocarditis as a possible side effect of the shots.
While acknowledging that some children probably will suffer the chest pain, shortness of breath or fluttering heartbeat of myocarditis, two panels of vaccine and immunology experts decided over the past two weeks that the benefits of COVID-19 vaccination outweigh this risk.
None of the 3,000 children ages 5 to 11 who participated in the Pfizer clinical trial developed myocarditis. No other serious side effects turned up in large numbers in the group or in the more than 200 million American adults and teenagers who have gotten COVID-19 vaccines since late last year.
Vaccine side effects mainly include short-term sore arms, headache, muscle pain and fatigue.
Children ages 5 to 11 will receive a dose one-third as large as given to adolescents and adults to minimize side effects. Studies show that their immune reaction is similar, despite the lower dose, and that the vaccine is more than 90% effective at preventing coronavirus infections in the age group.
An expert in myocarditis who spoke before two federal advisory panels said the low risk for the condition should not keep people from vaccinating their children against COVID-19.
“Getting COVID I think is much riskier to the heart than getting this vaccine, no matter what age and sex you are,” Dr. Matthew Oster, a pediatric cardiologist with Children’s Healthcare of Atlanta, told an advisory committee Tuesday. “The risk of having some sort of bad heart involvement is much higher if you get COVID than if you get this vaccine.”
Oster said children ages 5 to 11 are generally less likely than teens to develop myocarditis, and he expects rates in children after vaccination will be lower, too.
“I believe it is less likely that the 5- to 11-year-olds will have myocarditis (after vaccination), although we will watch and see for sure,” he said. “I don’t think it will be nearly to the extent that the older adolescents and young adults have.”
Since early in the pandemic, it has been clear that an infection with the SARS-CoV-2 virus, like many other pathogens, can trigger myocarditis.
Vaccine experts were surprised earlier this year when surveillance systems began suggesting that a number of people were developing the condition within a month of their second shot.
The risk for myocarditis after vaccination varies with age and sex. Older adolescent males are at highest risk.
Among the vaccinated, roughly 69 out every 1 million 16-and 17-year-old males have developed the condition, compared with just 8 out of every 1 million females of the same age, government data shows. By the mid- to late-20s, the rate falls to about 11 out of every 1 million males and 1 in 1 million females.
A large database outside the government found even lower rates of myocarditis in recently vaccinated people.
Overall, 19 people per 1 million experience myocarditis after getting the COVID-19 vaccine – pretty much the same as the general population, according to data from the Epic Health Research Network, which includes a large database of electronic medical records.
Epic researchers examined records of 15 million people vaccinated between Dec. 11, 2020, and June 9, 2021. While specific cases of myocarditis among the vaccinated get a lot of attention, “when you look at the big numbers, it’s just not that different from the normal baseline rate,” Dr. Christopher Alban, vice president of clinical informatics at Epic, said in an interview Wednesday.
“The unique thing about this is it’s a very large data set,” said his colleague Dr. Howard Bregman, director of clinical informatics. “We were able to compare apples to apples by saying the rate as we calculated it was compared to a rate before COVID. In that context, it was close to baseline.”
Government data also suggests that there are different types of myocarditis, Oster told both advisory panels.
He described three manifestations of myocarditis. The first, which doctors have long been familiar with and which Oster called “classic myocarditis,” follows infection with viruses, bacteria, protozoa or parasites. It can also be caused by drug sensitivities, toxins and autoimmune diseases.
Of those with classic myocarditis, more than two-thirds are males, and the risk is highest in the first year of life, probably because of genetic causes, Oster said, and in the late-teens and early 20s, which has been linked to high levels of the hormone testosterone.
The second form of myocarditis follows a condition called multisystem inflammatory syndrome, seen in both children and adults after a COVID-19 infection. Eight percent to 9% of people with the syndrome develop myocarditis, according to data Oster presented.
The third, seemingly distinct version, follows vaccination and appears to be milder and shorter-lasting, Oster said.
Classic myocarditis after infection can lead to serious, lingering effects and even death, Oster told the Centers for Disease Control and Prevention advisory panel Tuesday. “We don’t think this vaccine-induced myocarditis has nearly the same acute outcomes.”
Of 1,640 possible cases reported to a government reporting system, 877 have so far met the CDC case definition of myocarditis, and more are still to be investigated. Of those, Oster said, 34 didn’t require hospitalization, and more than three-quarters of those who did were released within a few days. No deaths were linked to this vaccine-associated myocarditis.
Of 16 adolescents who developed myocarditis after receiving the Pfizer-BioNTech vaccine, most of them this summer, 31% were considered fully recovered and did not need to take medication or restrict their exercise. One-quarter still had symptoms and 13% were still taking medication. (The Pfizer-BioNTech vaccine is the only one authorized for use in minors.)
Of 14 adults ages 18 to 39 who developed myocarditis after receiving the Pfizer-BioNTech vaccine, 43% were considered fully recovered and 29% were still taking medication. Of 18 adults who developed myocarditis after receiving the Moderna vaccine, half were considered fully recovered and 39% were still on medication, according to data Oster presented.
It’s not clear whether any of these people will have long-term complications, Oster said, but 91% of cardiologists or health care providers interviewed about their patients with vaccine-induced myocarditis indicated that the person was “fully” or “probably” recovered.
The American Heart Association and American College of Cardiology suggest that anyone who has myocarditis avoid strenuous physical activity, including competitive sports.
Oster also said he has not seen an increased risk for myocarditis among people with congenital heart disease. He said he tells families of children with heart disease “I am much more worried about what would happen to their child if they got COVID than I am if they were to get this vaccine.”
Contact Karen Weintraub at kweintraub@usatoday.com.
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