Student Well-Being

FDA Says Vaccine Benefits Outweigh Myocarditis Risks. Here Are the Facts

By Sarah D. Sparks — October 26, 2021 3 min read
Image of a young boy in a pediatrician's office.
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Which is more likely to put children in the hospital: COVID-19, or heart inflammation related to the vaccine to prevent it?

Even as the latest wave of the pandemic lessens, the coronavirus remains more dangerous, according to experts at the U.S. Food and Drug Administration, which convened an advisory panel Tuesday to review data on the Pfizer-BioNTech vaccine for children ages 5-11; the panel voted to endorse authorizing the vaccine 17-1, judging its benefits outweigh recent concerns about rare heart-related side effects.

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This October 2021 photo provided by Pfizer shows kid-sized doses of its COVID-19 vaccine in Puurs, Belgium. The vaccine appear safe and nearly 91% effective at preventing symptomatic infections in 5- to 11-year-olds, according to study details released Oct. 22, 2021, as the U.S. considers opening vaccinations to that age group.
Kid-sized doses of the COVID-19 vaccine developed by Pfizer and BioNTech. An FDA advisory committee has recommended that the vaccine be approved for emergency use in 5- to 11-year-old children.
Pfizer via AP

Heart inflammation was the most-concerning vaccine side effect both in the meeting and in public debates. But what exactly is it, and how likely is it to cause problems for young people?

What are myocarditis and pericarditis?

Myocarditis is inflammation of the heart muscle, while pericarditis is inflammation of the tissue surrounding the heart, and scientists describing vaccine side effects tend to use them both together. In children, both may trigger fever, chest pain, shortness of breath or fainting, and abnormal heart rhythms or feelings of a racing or pounding heart.

Viral infections—including German measles (rubella), fifth disease, and COVID-19 itself—are among the most common causes of the heart conditions, though the conditions are also associated with other kinds of infections and allergic reactions to chemicals or drugs.

On average, for every 100,000 people, about 10 to 20 people develop myocarditis each year, though boys—particularly adolescent boys—are much more likely to develop the conditions than girls. Myocarditis has also been found to be more common among children who develop COVID-related multisystem inflammatory syndrome, or MIS-C, a rare immune disorder.

How dangerous are myocarditis and pericarditis?

The most-severe cases can cause permanent heart damage, leading to permanent abnormal heart rhythms, heart attacks or strokes, or even cardiac arrest and death. However, the vast majority of cases have mild symptoms that go away in a few weeks.
In one study, three-quarters of vaccine-related myocarditis cases had mild symptoms, while 3 percent of cases were acute.

What effect do COVID-19 vaccines have on myocarditis risks?

Messenger RNA vaccines, like those developed by Pfizer-BioNTech and Moderna, do not use viral particles, but cause the body to make and recognize proteins associated with the virus to trigger an immune response. While scientists do not yet know exactly how this response goes wrong, scientists think heart inflammation could be caused by the immune system overreacting or improperly reacting to the protein.

A full two-dose course of either m-RNA vaccine has been shown to raise the risk that adolescents, particularly boys, will develop heart inflammation.

Dr. Hong Yang, senior advisor for benefit-risk assessment in the office of biostatistics and epidemiology at FDA’s Center for Biologics Evaluation and Research, explained in a presentation Tuesday that her group has modeled the risks and benefits of the vaccine at different levels of effectiveness and with infection rates ranging from the June low (before the Delta variant took over) to the peak of the most recent wave in September.

The researchers found that at current infection rates, vaccines could prevent nearly 45,800 COVID-19 cases and nearly 200 hospital stays for each million children ages 5-11 who are vaccinated. In comparison, they estimated about 106 extra cases of heart inflammation and 92 extra hospitalizations would be linked to the vaccines.

But she warned that overall hospital numbers don’t give the full picture, as the median hospital stay for COVID-19 was six days, compared to only one day for vaccine-related myocarditis, and no children died as a result of the vaccine-related heart inflammations.

“When we compare the benefits and risks side by side, we need to keep in mind that the clinical implications of hospitalizations and ICU stays due to COVID-19 are much more, very different from those due to vaccine-related myocarditis,” she said. “The former require much more extensive clinical care … and later monitoring patients’ conditions as a precaution.”

Chart: Weighing Risks. Across multiple scenarios by the Food and Drug Administration, the baseline risks for boys were worse if they became infected with COVID-19 than if they developed a vaccine-related heart inflammation. The risks for girls, and for both if another wave of COVID hits, were even more skewed in favor of the vaccine. Source: U.S. Food & Drug Administration

“For all three age groups [5-11, 12-15, and 16-17], the benefits clearly outweigh the risks,” Yang said.

Yang noted, however, that the risk calculus may change once the pandemic is significantly under control. If COVID-19 case rates drop to only 5 percent of the Sept. 11 rate—say, 13 per 100,000 for children 5-11 and 15 per 100,000 for those ages 12-15—then the risks may outweigh the benefits for adolescent boys, though not for girls.

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