Publisher Health

Pfizer and its partner BioNTech are expected as soon as Tuesday to ask the Food and Drug Administration to authorize a coronavirus vaccine for children under 5 years old as a two-dose regimen while they continue to research how well three doses work.

Federal regulators are eager to review the data in hopes of authorizing shots for young children on an emergency basis as early as the end of February, according to multiple people familiar with the discussions, who were not authorized to speak publicly. If Pfizer waited for data on a three-dose regimen, the data would not be submitted until late March and the vaccine might not be authorized for that age group until late spring.

Federal officials and Pfizer executives had been suggesting for days that an application for emergency authorization of a vaccine for children as young as 6 months was in the works. Every age group above that is eligible for shots, and the highly contagious Omicron variant has led to a sharp rise in infections among all ages, including children. There are more than 19 million Americans under 5 years old.

Scott Gottlieb, a Pfizer board member and former commissioner of the Food and Drug Administration, told CBS News on Sunday that the vaccine might be authorized as soon as March for the youngest age group. The development was first reported by The Washington Post.

Parents of younger children have been eager to see Pfizer and federal regulators move to make the shots available. Many families have said they are in limbo waiting out the Omicron wave and grappling with day care closures and child care crises.

Federal officials are eager to begin a vaccination program for young children because the Pfizer-BioNTech studies showed two doses provided a notable level of protection against Covid-19 with no safety concerns, according to people who have been briefed on the data. Officials expect the regimen will eventually include three doses.

Pfizer and BioNTech in mid-December announced that children 6 months to two years old who were given two doses of the vaccine at a tenth of the strength of adult doses produced an immune response comparable to that of young people ages 16 to 25. But among children ages 2 to 4, the response was less robust.

The setback prompted the companies to test a third low dose of the shot in young children. Rather than wait for those results, federal regulators took the unusual approach of encouraging Pfizer to apply for authorization for a two-dose regimen to begin protecting children from the Omicron variant and other possible subsequent mutations, according to four people familiar with the strategy.

Even though young children largely do well in combating the virus, the American Academy of Pediatrics says that the Omicron variant has intensified the threat of Covid-19 in children under 5.

“Sadly, we are seeing the rates of hospitalizations increasing for children 0 to 4, children who are not yet currently eligible for Covid-19 vaccination,” Dr. Rochelle Walensky, the director of the Centers for Disease Control and Prevention, told reporters this month. She said the high rate of transmission of the Omicron variant was likely to blame.

The F.D.A. and C.D.C. are both expected to convene committees of outside vaccine advisers before a decision on whether to clear the shots. That will give independent experts a chance to discuss the data the companies have gathered. Most senior federal health officials are strongly behind the strategy, two officials said, but they want the outside experts to weigh in.

Kathrin Jansen, Pfizer’s head of vaccine research, said in December that the company would seek F.D.A. clearance for three doses for young children, a strategy that she said would allow for “a consistent three-dose vaccine approach for all ages.” The company switched its plan because the F.D.A. was pressing for more urgent action, two people said. If authorized, young children will receive their second dose three weeks after the first, and a third dose two months after that.

The C.D.C. now considers three doses of the vaccine to be an “up-to-date” regimen for those eligible for extra shots, including those 12 and up. Regulators have authorized booster doses given five months after second injections. Children as young as 5 who have weakened immune systems are also eligible for extra shots.

The deliberations in the coming weeks could affect how quickly parents get their youngest children vaccinated. The pace of vaccination for America’s 28 million children between 5 and 11 remains even lower than health experts had feared. Roughly 30 percent of children in that age group have received at least one dose, according to C.D.C. data.

The reasons more young children have not gotten shots vary. Some parents are put off by misinformation about the vaccine; others do not believe the virus is enough of a threat to vaccinate their children. Some simply have not yet found the time to take their children in for shots, health officials report.

The C.D.C. released research in late December that showed very few reports of serious problems among children 5 to 11 who had received Pfizer-BioNTech shots. Another study of hundreds of pediatric hospitalizations in six cities last summer, released by the agency, found that nearly all of the children who became seriously ill had not been fully vaccinated.