Vaccine makers Pfizer and BioNTech said they will complete their submission for emergency use authorization of their Covid-19 vaccine for children under the age of 5 this week after a study of a third dose found it improves the efficacy of the vaccine.
The companies said that, with three doses, the vaccine performed about as well in young children as it does in adults. The vaccine was well tolerated, induced a strong immune response and was 80.3% effective at preventing Covid infections at a time when the Omicron variant of the SARS-CoV-2 virus was circulating.
“The study suggests that a low 3-[microgram] dose of our vaccine … provides young children with a high level of protection against the recent Covid-19 strains,” Ugur Sahin, CEO and co-founder of BioNTech, said in a statement.
Children six months to four years of age are the last group for which Covid vaccines have yet to be authorized. The Food and Drug Administration has been under pressure from anxious and frustrated parents to fill this gap.
Moderna has already completed a submission for its Covid vaccine for children aged 6 months to 6 years, based on study of a two-dose vaccine. The two 25 microgram shots, given four weeks apart, generated immune responses similar to what was seen in adults 18 to 25 years old after two doses. But the vaccine efficacy was 43.7% in children aged 6- to 24-months and 37.5% in children aged 2 to under 6 years. When the company announced the results in March it said it was going to study the efficacy of a booster shot in these age group, but results have not been made public to date.
The FDA announced recently it has asked members of its vaccines advisory group, the Vaccines and Related Biological Products Advisory Committee, to hold three dates in June for possible meetings on the pediatric vaccines. The first of the dates is June 8, suggesting that if the FDA can complete one or both of these reviews in time and, if they are favorable, an emergency use authorization for a Covid vaccine for children under five could be approved by the end of the second week of June or the beginning of the third week.
The Pfizer dosage for children under age 5 is one-tenth of the dose used in its vaccine for adults. As with adults, the first two doses are given 21 days apart, but the third dose is given at least two months after receipt of the second. In adults, the third dose is given at least five months after the second dose.
The Phase 2/3 trial was conducted in 1,678 children. A month after receipt of the third dose, antibody titers from a subset of the children were compared to those seen in people aged 16 to 25 years after they had received two doses of the vaccine. The antibody levels were “non-inferior” in children ages 6 to 24 months, and also among those children ages 2- to 4-years old, the companies said.
“Our Covid-19 vaccine has been studied in thousands of children and adolescents, and we are pleased that our formulation for the youngest children, which we carefully selected to be one-tenth of the dose strength for adults, was well tolerated and produced a strong immune response,” Albert Bourla, Pfizer chairman and CEO, said in a statement.
Pfizer and BioNTech had hoped to get its vaccine authorized for children under 5 months ago. But the companies announced late last year that the two-dose regimen it tested did not generate a similar level of protection in the children ages 2 to 4 as it did in young adults ages 16 to 25, the immunogenicity measurement the FDA had agreed to use as a sign that the vaccine was likely protective. Paradoxically, the same dose did induce an adequate response in children ages 6 to 23 months.
At the time, the company announced it would test the impact of adding a third dose before applying to the FDA for authorization. But in early February, the agency asked Pfizer and BioNTech to submit their data on a rolling basis, suggesting they might move to allow the first two doses to be used while awaiting the results of the third-dose study.
Parents keen to vaccinate their children during the early crush of the Omicron wave were thrilled, but some experts worried that the move could further erode confidence in the vaccines among parents who have been reluctant to vaccinate children against Covid. Only about 28% of children ages 5 to 11 have received two doses of Covid vaccine. (Boosters for this age group were only authorized last week.)
In mid-February, the FDA announced it would wait for the third-dose data before reviewing the Pfizer-BioNTech application for authorization of its vaccine for children under the age of 5.
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