Pfizer Inc. and partner BioNTech SE said they have begun submitting data to U.S. regulators for authorization of their COVID-19 vaccine in younger children, hastening an effort to get shots to more kids after the omicron wave caused pediatric infections to jump.

The companies said in a statement that they have started a so-called rolling submission with the U.S. Food and Drug Administration seeking an emergency authorization for the vaccine in children 6 months to four years of age.

The clearance request came earlier than expected. Data that was released by the companies in December suggested that the ability of two doses to prevent infection was mixed and that the companies would need to collect more evidence before asking for an authorization. The companies said at the time that they would study a third dose and if successful, seek a U.S. emergency authorization in the first half of 2022.

However, Pfizer and BioNTech accelerated that timetable at the request of regulators. The FDA asked the drugmakers to submit data on two doses of the shot as part of a three-dose series, according to the statement. Data on a third dose given eight weeks after the second shot are expected in coming months and will also be sent to regulators, the companies said.

Parents have been pushing the Biden administration and the companies to move faster to get shots cleared for younger kids. With cases surging this winter, more kids have been infected with the virus, complicating child care and parents’ efforts to remain at work. At the same time, however, there are signs that families are more wary of getting shots for younger kids.

While vaccines have been available for children ages 5 to 11 for several months, vaccination rates in that group remain lower than in older demographics even amid signs that the omicron strain leaves kids at greater risk of disease. Virus cases among children have risen since omicron was first detected in the U.S. in December, with pediatric hospitalizations reaching a record at the end of last year.

More Shots

In December, Pfizer vaccine executive Kathrin Jansen said that limiting the spread of the more infectious omicron variant, which currently accounts for almost all COVID-19 cases, “may only be possible with three or more doses.”

Three shots are now recommended by the Centers for Disease Control and Prevention for everyone 12 and older, and it is expected that third shots will be cleared for 5 and up soon. While U.S. regulators consider anyone who has received two doses of a messenger RNA shot to be fully vaccinated, studies have shown three doses are more effective at shielding against an omicron infection.

Anthony Fauci, President Joe Biden’s top adviser on the pandemic, said last week that he thought the Pfizer vaccine for younger kids would be a three-shot regimen. Fauci said at a news conference that the FDA is “very scrupulous” in reviewing vaccines, especially for children, and that if shots were to be cleared “we can be certain that they will be safe and that they will be effective.”

While a faster clearance is likely to satisfy parents who are eager to vaccinate their kids, it could also exacerbate uneasiness among those who have been more uncertain about shots for children. Recent CDC studies showed that the shots caused few side effects in the 5-to-11 age group and were overwhelmingly effective at keeping adolescents out of the hospital.

The U.S. immunization effort has been leveling off for all ages. Some 68% of people 5 years and older are considered fully vaccinated, according to CDC data, while 42% of those who are eligible have received a booster shot as of Monday.

The FDA is expected to convene a panel of expert advisers to consider the evidence on the Pfizer shot for younger kids, likely later this month. The agency isn’t bound by the group’s advice but generally adheres to it. A group of experts that advises the CDC on vaccine policies is also likely to meet.