Pfizer authorization allows for 'more careful review' of Moderna vaccine for teens

There have been rare reports of myocarditis and pericarditis among people who have received a COVID-19 messenger RNA vaccine, with cases occurring especially among male adolescents and young adults, according to the CDC.

Researchers last week reported in The BMJ that the rate of myocarditis among almost 5 million vaccinated people in Denmark was higher among those who received the Moderna vaccine than the one made by Pfizer-BioNTech, but that the absolute number of cases was low.

“I know a lot of parents have questions about myocarditis. Fortunately, it's been mild and self-limiting,” Henry H. Bernstein, DO, a pediatrician at North Shore University Hospital in Manhasset, New York, told Healio.

In fact, the issue became evident only after the Pfizer-BioNTech vaccine was granted an emergency use authorization (EUA) by the FDA, according to Mariska S. Kemna, MD, a pediatric cardiologist and professor of pediatrics at Seattle Children's Hospital.

“Since vaccine-related myocarditis is so rare, occurring in one in 5,000 to 10,000 young males, it actually didn’t show up as a side effect in the initial trials,” Kemna told Healio.

Still, the issue led the FDA to delay its decision on Moderna’s application for an EUA that would make the vaccine available to children aged 12 to 17 years in the U.S. Because of the delay, Moderna said it would postpone filing another EUA request for a 50 µg half-dose of the vaccine for children aged 6 to 11 years.

Kenma said the fact that the Pfizer vaccine is already authorized for children allows for a “more careful review” of Moderna’s formula.

“Since there already is a similar vaccine available for the teen population, the FDA is able to take more time for a careful review, as there is less of a sense of pandemic urgency,” Kemna said.

She added that although Moderna’s pediatric vaccine is used in Europe, a higher rate of myocarditis compared with Pfizer’s vaccine “may have caused some hesitancy [for] the FDA.”

“It has also led some European countries, such as Norway and Sweden, to no longer offer Moderna to any males younger than 30,” Kemna said.

Although no conclusive evidence has been found regarding why the vaccines may cause myocarditis, Kemna suggested that researchers look at the Moderna dose.

“While we don’t fully understand why Moderna’s vaccine would incur a higher risk of myocarditis, it may be dose related since Moderna’s vaccine dose (100 µg) is significantly higher than Pfizer’s (30 µg),” Kemna said.

She suggested that young men could potentially benefit from lower doses of both vaccines, or a vaccination schedule with a longer interval between the first and second dose to lower their risk for vaccine-associate myocarditis.

“For example, the immune system of a teenager is wildly different from the immune system of a 70-year-old, yet, currently, both receive the same vaccine dose and schedule,” Kemna said. “On the other hand, children between 5 and 11 years old receive 10 µg of the Pfizer vaccine, whereas 12- to 18-year-olds receive 30 µg, even though their immune systems are probably equally responsive.

“The coming months will reveal whether the pediatric age group between 5 and 11 years old that is currently being vaccinated with the lower vaccine dose will sustain the same risk of myocarditis as the teenagers. If not, a strong argument can be made to lower the vaccine doses in teens so they can be protected from both COVID-19, as well as vaccine-related myocarditis.”

Nevertheless, she said, it will still be crucial for all eligible children to receive the vaccine, regardless of risks.

“It remains important to recognize that the risk of cardiovascular complications, even myocarditis, is much higher from COVID-19 than from a vaccination with an mRNA COVID vaccine,” Kemna said.

References:

CDC. Myocarditis and pericarditis after mRNA COVID-19 vaccination. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/myocarditis.html. Accessed Dec. 21, 2021.

Husby A, et al. BMJ. 2021;doi:10.1136/bmj-2021-068665.