Pfizer Inc has begun submitting data to federal regulators as part of the process to win U.S. emergency use authorization (EUA) of its COVID-19 vaccine for children under age 5, Bloomberg reported on Tuesday.

“The rolling submission of data asks regulators to clear the shot as a two-dose vaccine, though it’s expected that ultimately a three-shot regimen may become standard,” the Bloomberg report said, citing unnamed people familiar with the data.

The vaccine from Pfizer and partner BioNTech is already approved for emergency use in children in the United States ages 5 and older. It has full approval for adults.

Representatives for Pfizer, as well as for the U.S. Food and Drug Administration and the Department of Health and Human Services, could not immediately be reached for comment on the report.

The Washington Post on Monday said the companies could seek an EUA for children aged 6 months to 4-years-old as soon as Tuesday.

Pfizer, in a statement late on Monday, said it had not yet sought approval and was “continuing to collect and analyze data from both two and three doses in our younger age cohort.”

The FDA has also authorized a third booster dose of the Pfizer/BioNTech shot for adults and children aged 12 and older. It gave the green light for a two-dose vaccine for children ages 5 to 11.

The companies previously said they needed to amend their study because those under 5 did not have as strong an immune response as the larger dose older children received.

Last month, Pfizer said it expected to have those results by April. The rolling submission, if approved, would allow the company and health officials to start moving forward with shots for those under age 5 until the rest of the data becomes available.