WASHINGTON, (Reuters) –Pfizer Inc began submitting data for federal regulators in the course of the U.S. emergency authorization (EUA), of COVID-19 vaccine to children below 5 years old Bloomberg reported 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 can be purchased from Pfizer (NYSE:) And partner BioNTech are already approved in America for children 5 years and over. The product is fully approved for adult use.

Pfizer Representatives, the U.S. Food and Drug Administration, and the Department of Health and Human Services were not available for comment immediately.

The Washington Post said Monday that companies might seek EUAs for children 6 months-to-4 years of age as soon as Tuesday.

Pfizer released a late Monday statement saying it hadn’t yet applied for approval but was continuing to “collect and analyze data from both the two and three doses within our younger cohort.”

FDA also approved a third booster dose for the Pfizer/BioNTech shot, both for children and adults 12 years and over. A two-dose vaccine was approved by the FDA for children aged 5 to 11.

Previous studies had shown that children under five did not respond as well to higher doses of immunotherapy than older children.

Pfizer stated last month that it expects to receive those results in April. If approved by Pfizer, the rolling submission would enable the company to move forward with shots for children under 5 years old until more data is available.