Moderna’s coronavirus vaccine elicits a strong immune response in children ages 6 to 11, researchers reported Wednesday, another sign in what has become a long and winding road to protect young children against the virus, even when cases rise again.
On Monday, Moderna applied to the Food and Drug Administration for authorization to use the vaccine in this age group. But the authorization, if granted, is unlikely to add much to low immunization rates among young children.
The Pfizer-BioNTech vaccine has been available to children ages 5 to 11 since November, but as of Wednesday, only 28.7 percent had received two doses. There is no coronavirus vaccine available for children under 5 years of age, forcing parents to rely on less reliable protective measures.
Last month, Moderna applied to the FDA to authorize its vaccine for use in children 6 months to 6 years old. The agency is already reviewing the company’s data on adolescents and is expected to decide on the use of the Moderna vaccine in children of all ages in June.
In February, Pfizer and BioNTech also applied to license their vaccine for use in younger children, but withdrew the application after data suggested that two doses did not produce adequate protection against the Omicron variant.
The companies are banking on a third dose to boost immunity in children, and the FDA is also expected to review that data in June.
“We really can’t do it this way in the future, we can’t leave children to last,” said Dr. Sallie Permar, a pediatric vaccine expert at Weill Cornell Medicine in New York.
The process has been particularly confusing and unfair to parents of younger children, who still don’t have access to a vaccine more than two years into the pandemic, he said.
It has been nearly a year since Moderna applied for FDA authorization for use of its vaccine in adolescents ages 12 to 17. While the agency gave the Pfizer-BioNTech vaccine the go-ahead for use in that age group in just three weeks, the agency’s review of the Moderna vaccine had stalled.
The delay in authorization has been greater in the United States. Medicines regulators in Europe approved Moderna’s vaccine for adolescents ages 12 to 17 last summer and recommended approval for children ages 6 to 11.
Regulatory agencies in Canada and Australia have also licensed the Moderna vaccine for children 6 to 11 years of age.
In the United States, just over one in four of the 28 million children ages 5 to 11 have been vaccinated against the coronavirus. Parental reluctance appears to be due in part to the fact that infection is known to be less risky for children.
“The risk of a child contracting severe covid is much, much, much lower; let’s be honest about it,” said Dr. Ofer Levy, director of the precision vaccines program at Boston Children’s Hospital and an adviser to the FDA.
Still, he said he had just treated a child with leukemia who had been hospitalized for Covid. “Some children get severe covid, some end up in a hospital,” she said, adding that more than 1,500 children under the age of 18 have died so far in the pandemic.
“I’m not interested in mandates, but I think families should have the option to protect their youngest children,” said Dr. Levy.
In its trial, published in The New England Journal of Medicine, Moderna first tested different doses of its vaccine, choosing a 50 microgram dose, half the adult dose, for children ages 6 to 11. The researchers then randomly assigned more than 4,000 children. receive two injections 28 days apart.
Three quarters of the children received the vaccine and the rest received placebo injections of salt water. About half of the children were from communities of color. To measure the potency of the vaccine, the researchers measured the antibodies produced after immunization. (Pfizer’s vaccine trials were based on this same approach, called immunobridging.)
The children who received the vaccine produced slightly higher levels of antibodies than those seen in young adults, a promising sign. The trials were not large enough to test the ability of the vaccine to prevent serious illness or death.
But based on a small number of infections with the Delta variant among the participants, the researchers estimated that the vaccine was 88 percent effective against the infection.
“Immunoblotting is basically an educated guess that we take — that the same level of immunity will be just as protective in a younger age group as it was in an older age group,” Dr. Permar said. “So it’s nice when you can track that effectively as well.”
The injections seemed to cause only minor side effects, including pain at the injection site, headache and fatigue, and less often than in adults. About half of the children also had a fever for about a day.
That side effect can become a problem in children younger than 5 years, because high fevers in very young children require invasive tests to rule out dangerous bacterial infections, Dr. Permar said.
The trial was not large enough to detect rarer side effects, such as heart problems that have been seen in other age groups. The Pfizer-BioNTech vaccine appears to cause fewer cases of so-called myocarditis among young children than among adolescents or young adults.
Moderna’s trial measured the potency of the vaccine against the Delta variant, and researchers are still evaluating its performance against Omicron. All vaccines have been shown to be less effective, in all age groups, against the Omicron variant.
Independent scientists have reported that the Moderna vaccine provokes a strong immune response in children aged 7 to 11, and in adolescents, against the Omicron variant and other versions of the coronavirus.
But these antibodies seem to wane over time, as they do in adults. “Probably the performance of the vaccine, in terms of vaccine efficacy, is not going to be as high in real-world data,” Dr. Levy said.
Dr. Permar said she hoped the pandemic would bring a change in how vaccines are tested during an emergency.
“We need to think of a different way of approaching the inclusion of children and pregnant women in trials earlier,” he said. “And we have to be doing that now, because the next pandemic will be upon us sooner than we want.”