Pfizer and BioNTech said Monday that preliminary findings from a clinical trial involving children under the age of five showed that three doses of their coronavirus vaccine produced a strong enough immune response to meet criteria for regulatory authorization.
In a press release, the companies announced the results of a subset of a trial involving 1,678 children, ages 6 months through 4 years, saying the three-dose regimen was 80 percent effective in preventing symptomatic infection. No supporting data was disclosed and the companies did not say how many children were in the subgroup. A Pfizer spokeswoman said the detailed results of the trial will be released next month.
Both Pfizer and Moderna hope to receive approval soon to vaccinate the country’s youngest children. About 18 million children under the age of 5 are the only Americans not yet eligible for coronavirus vaccination, and parents’ expectations about when injections will be offered have been shattered repeatedly.
Pfizer and its partner BioNTech said the number of children in the study who received Covid was too small to make a definitive statement on efficacy. Only 10 children in the trial became ill with Covid after those in the vaccination group received the third dose. The clinical trial protocol specified that analysis of vaccine efficacy required at least 21 Covid cases. The companies said final efficacy data, a secondary endpoint for the clinical trial, would be shared “as soon as available.”
The Biden administration had hoped to offer vaccine doses to children under 5 as early as February. The Food and Drug Administration initially urged Pfizer to submit data on how well two doses worked for young children, but withdrew after Pfizer said two doses were not sufficiently effective in preventing symptomatic infection of the very infectious Omicron variant.
But Pfizer said the new results showed that three doses, with the third given at least two months after the second, stimulated the immune system to strongly protect against the virus, with no safety concerns. Researchers said the immune response of the subset of trial participants, measured one month after the third dose, compared favorably with that of people ages 16 to 25 who received two doses.
“We are pleased that our formulation for the youngest children, which we carefully selected to be one-tenth the dose strength for adults, was well tolerated and produced a strong immune response,” said Dr. Albert Bourla, CEO of Pfizer, in a statement. dr. Ugur Sahin, chief executive of BioNTech, said the companies would complete their FDA emergency approval application for the pediatric vaccine this week.
The new findings spark a competition between Moderna and Pfizer over which company will produce the best vaccine for the youngest Americans. Moderna suggests a two-dose regimen for children under 6 years of age, using a quarter of the strength of the adult dose. The company has indicated that it expects a third dose to be needed as a booster injection, but has not yet provided any information to the government.
The question of which vaccine works better will be submitted to a committee of outside FDA advisors at a meeting scheduled for June 15. With both Pfizer and Moderna proposing different dosing regimens for the youngest children and presenting different clinical trial results, the commission could influence regulators on which vaccine should be approved, or whether both merit approval.
In late April, Moderna applied for an emergency license for its pediatric vaccine after interim results showed that clinical trial participants had a similar immune response as young adults when given a dose one-fourth as strong.
Like Pfizer, the company said the results met the clinical trial’s criteria for success. Moderna has said the vaccine was found to be 51 percent effective against symptomatic infections in children under 2 years of age and 37 percent in children 2 to 5 years of age.
If Pfizer’s results are confirmed by later data, its efficacy would be better than Moderna’s. Both companies say their vaccines have similar side effects to other pediatric vaccines that have been used for decades.
Adeel Hassan reporting contributed.
