The Food and Drug Administration’s (FDA) advisory committee voted unanimously on June 14 to recommend the emergency-use authorization (EUA) of Moderna’s COVID-19 vaccine for children ages six to 17 years. If it’s also recommended by the U.S. Centers for Disease Control and Prevention (CDC), Moderna’s will be the second COVID-19 vaccine available to this age group. (The FDA and CDC previously issued an EUA for the Pfizer-BioNTech COVID-19 vaccine in October 2021 for children five years and older.)
Because the company submitted data that broke down the children into two age groups—from six to 11 years old, and 12 to 17 years old—the 22-member panel voted separately for the two populations. Each vote was unanimous that the benefits of vaccination outweighed the risks.
The committee’s recommendation is based on data submitted by Moderna’s scientists on the safety and efficacy of its two-dose vaccine for kids ages 6-17. Those studies found that the vaccine—which is the same one authorized for adults but in a smaller dose—is as effective at protecting children from getting seriously ill or dying from COVID-19 as it is at protecting adults, even against different variants of the virus.
The FDA’s panel of pediatric and immunology experts reviewed two studies conducted by Moderna in children, which showed that kids ages six to 17 generated levels of virus-neutralizing antibodies one month after their second dose that were equal to those produced by older adolescents and adults. Because the pediatric studies did not include a long follow-up time, FDA scientists inferred from this data that those levels of antibodies—measured one month after the second dose—would be sufficient to protect children from severe disease by comparing them to antibody levels generated by adults. Studies have demonstrated that adults with those same levels of neutralizing antibodies are about 90% less likely to get severely ill, need hospitalization, or die from COVID-19 than unvaccinated adults. No children in the studies developed severe disease or died from COVID-19.
Moderna’s pediatric vaccine comes in two different doses, depending on children’s ages. Older children ages 12 to 17 would receive the same dose as adults, 100 micrograms per shot. Children ages six to 11 would receive half that dose in each of their two shots; the company’s studies found that the lower dose led to sufficient levels of virus-fighting antibodies and lowered the risk of potential side effects.
One issue the panel considered was the fact that vaccine efficacy means different things for the different age groups. Because Moderna tested its vaccine in children moving from the oldest to the youngest—and only vaccinated younger children after the shot proved to be safe in older kids—the variants to which the children might have been exposed changed over time. Most of the participants were enrolled in the U.S., and waves of different SARS-CoV-2 variants swept through the country as each age group was tested. The data of vaccine efficacy in adults, to which the vaccine efficacy in children were compared, were also generated before the variants emerged and reflect immunity to the original SARS-CoV-2 virus.
The vaccine efficacy against COVID-19 symptoms for children ages 12 to 17 years was 93% when the original SARS-CoV-2 strain and the first variant, Alpha, were circulating, while the vaccine efficacy was 76.8% among children six to 11 years old who were vaccinated during the Delta wave. Among the youngest children ages two to five, who were tested more recently during the Omicron wave, the vaccine efficacy was 36.8%; among toddlers six months to two years, it was 50.6%. The data mirror those found among vaccinated adults during each of those variant waves.
Some members of the committee—including Dr. Paul Offit, professor of pediatrics at the Children’s Hospital of Philadelphia—raised concerns that the lower efficacy against Omicron would mean that children, like adults, would need an additional dose to maintain immunity at sufficient levels to protect them against serious disease. “This is a three-dose vaccine if it is to be effective against serious Omicron disease,” he said. However, the question of how many doses would be sufficient for protection was not the question on which the committee members voted. Their task was to weigh the benefits and risks of Moderna’s two-dose series to determine if those are safe and effective.
In its review of the data, the FDA’s scientists determined that the vaccine was safe for kids ages 6-17, with similar types and rates of adverse reactions as those reported among adults. The safety of the vaccines was one reason why the FDA delayed reviewing Moderna’s vaccine data for this age group, which were submitted in June 2021. After Moderna submitted this data, studies showed that adolescents who were vaccinated with Moderna’s shot in the U.S. and other countries—including in the U.K., Europe, and Canada—had a two to seven-fold higher risk of developing dangerous inflammation of the heart tissues, known as myocarditis, compared to children vaccinated with Pfizer-BioNTech’s shot, which is made with similar mRNA technology and was authorized in the U.S. in May 2021. The risk appeared highest among young males between ages 18 and 24, and the CDC launched an investigation to determine if Moderna’s vaccine posed any higher risk compared to Pfizer-BioNTech’s. The most recent data from CDC’s database that monitors side effects through May 2022 “do not support a difference in myocarditis/pericarditis risk for [Moderna’s vaccine] compared to [Pfizer-BioNTech’s vaccine],” the FDA review determined.
Moderna also requested authorization of its vaccine at a lower dose for children ages six months old to six years, which the same FDA committee will review on June 15. During that meeting, the experts will also review data from Pfizer-BioNTech about its vaccine in a similar age group, from ages six months to four years.
Having two vaccines for the pediatric population would provide more choice for parents eager to get their children vaccinated, and also potentially create more confusion if pediatricians or hospitals and pharmacies only stock one manufacturer’s shots. Studies have shown that in adults, mixing and matching from the two different mRNA vaccines made by Pfizer-BioNTech and Moderna is safe and effective, but those studies have not been conducted specifically in children yet (although some experts presume that the shots can be safely interchanged in the pediatric population as well).
If the CDC panel also recommends the Moderna vaccine for this pediatric population, the U.S. government says doses could be shipped to hospitals, doctors’ offices, and pharmacies beginning the week of June 20.
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