Pfizer and BioNTech have requested emergency authorization from the Food and Drug Administration to use their COVID-19 vaccine in children ages 6 months to 5 years, the companies announced Tuesday, following Monday reports.

If authorized, Pfizer’s would be the first COVID vaccine available for kids under five, CNN reports. The two companies are also “continuing to test a three-dose version of the vaccine in this younger age group.”

The youngest kids will receive the smallest dose: 3 micrograms a shot.

Federal regulators encouraged Pfizer to submit data for authorization for the two-dose vaccine, rather than wait on data for three doses, which could have potentially delayed the process until March, CNN notes. The two-dose regimen notably produced “disappointing results in some children during testing,” leading researchers to believe another dose may eventually be required for full protection, reports The Wall Street Journal.

“If the goal of the vaccine is to get baseline immunity in the kids — to prevent really bad outcomes and you’re really not using the vaccine as a tool to prevent infection in the first place — two doses could do that,” former FDA commissioner and current Pfizer board member Dr. Scott Gottlieb said Sunday, per CNN. “I think that may be why federal health officials are rethinking this.”

On that note, the FDA reportedly encouraged Pfizer to forge ahead with authorization of the two-shot regimen so kids would be eligible for a third dose later, should it prove safe and effective, the Journal adds. There were no serious safety concerns during testing, the companies said.

There are over 19 million Americans under 5 years old, The New York Times reports.