Moderna’s coronavirus vaccine elicits a strong immune response in children ages 6 to 11, researchers reported Wednesday — another signpost in what has become a long and winding road to protect young children from the virus, even as cases rise again.
On Monday, Moderna applied to the Food and Drug Administration for approval to use the vaccine in this age group. But authorization, if granted, is unlikely to increase the low vaccination rates of young children much.
The Pfizer-BioNTech vaccine has been available for 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 at all for children under the age of 5, forcing parents to rely on less reliable protective measures.
Last month, Moderna asked the FDA for approval for the 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 make a decision in June on the use of the Moderna vaccine in children of all ages.
In February, Pfizer and BioNTech also applied for their vaccine for use in the youngest children, but withdrew the application after data suggested two doses did not provide adequate protection against the Omicron variant.
The companies are counting 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 kids to last,” says Dr. Sallie Permar, a pediatric vaccine expert at Weill Cornell Medicine in New York.
The process has been particularly confusing and unfair for parents of the youngest children, who still have no access to a vaccine more than two years after the pandemic, she said.
It’s been nearly a year since Moderna asked for FDA approval to use its vaccine in adolescents ages 12 to 17. While the agency gave the green light to Pfizer-BioNTech’s vaccine for use in that age group in just three weeks, the agency’s review of Moderna’s vaccine had stalled.
The delay in approval has been longest in the United States. European drug regulators approved the Moderna vaccine for adolescents ages 12 to 17 last summer and recommended approval for children ages 6 to 11.
Regulators in Canada and Australia have also approved the Moderna vaccine for 6 to 11 year olds.
In the United States, just over one in four of the 28 million children ages 5 to 11 have been vaccinated against the coronavirus. The reluctance of parents seems to stem in part from the fact that the infection is known to be less risky for children.
“The risk of a child getting severe Covid virus is much, much, much lower — let’s be honest about that,” says Dr. Ofer Levy, director of the precision vaccine program at Boston Children’s Hospital and advisor 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 hospital,” he said, adding that more than 1,500 children under the age of 18 have died in the pandemic so far.
“I don’t like mandates, but I do believe that families should have the ability to protect their youngest,” said Dr. levy.
In her trial, published in The New England Journal of Medicine, Moderna first tested several doses of her vaccine and chose a 50 microgram dose — half the adult dose — for children ages 6 to 11. The researchers then randomly assigned more than 4,000 children to receive two shots 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 came from communities of color. To measure the vaccine’s potency, the researchers measured antibodies produced after immunization. (Pfizer’s vaccine trials were based on the same approach, called immunobridging.)
The children who received the vaccine produced antibody levels slightly higher than those seen in young adults, a promising sign. The trials were not large enough to assess the vaccine’s ability to prevent serious illness or death.
But based on small numbers of Delta variant infections among the participants, the researchers estimated that the vaccine had an 88 percent efficacy against infection.
“Immunobridging is basically an educated guess we take — that the same level of immunity will be just as protective in a younger age group as it is in an older age group,” said Dr. permar. “So it’s nice if you can also follow that up with efficacy.”
The injections seemed to cause only minor side effects — including injection site pain, 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 under age 5, because high fevers in very young children require invasive testing to rule out dangerous bacterial infections, said Dr. permar.
The study was not large enough to detect rarer side effects, such as the heart problems seen in other age groups. The Pfizer-BioNTech vaccine appears to cause fewer cases of so-called myocarditis in young children than in adolescents or young adults.
Moderna’s trial measured the vaccine’s potency against the Delta variant, and the researchers are still assessing its performance against Omicron. All vaccines have been shown to be less effective against the Omicron variant in all age groups.
Independent scientists have reported that the Moderna vaccine elicits a strong immune response in children ages 7 to 11 and in adolescents against the Omicron variant and other versions of the coronavirus.
But these antibodies seem to decrease over time, as they do in adults. “Probably the vaccine performance, in terms of vaccine efficacy, will not be as high in real world data,” said Dr. levy.
dr. Permar said she hoped the pandemic will change the way vaccines are evaluated during an emergency.
“We need to think of another way to approach children and pregnant women earlier in trials,” she said. “And we need to do that now, because the next pandemic is coming before we want to.”