Pfizer and its partner, BioNTech, have officially submitted data to the U.S. Food and Drug Administration (FDA) to have its vaccine authorized for use in children aged six months to four years old.

The company announced the move on Tuesday afternoon, following reports earlier in the day that the regulatory agency was urging them to submit an application soon. 

Despite the push from regulators to expand eligibility for the shots to include young children, the controversial move would make the U.S. the only nation to jab children under one years old for Covid.

It would also make the U.S. the world's lone nation to approve the Pfizer vaccine for children under five. Some doubt the shot is needed for people that young due to the little risk they face from the virus.

The vaccine regimen for young children will include two doses of three micrograms each. For comparison, the jab for people 12 and older is 30 micrograms, and the shot for kids five to 11 is 10 micrograms. 

A third dose was added for younger children in December, when early clinical trial results showed that kids aged three and four were showing little immune response to just the two doses.

This initial application filed by the New York City-based company only includes the first two shots, with the third expected to be submitted later.

'Data on a third dose given at least 8 weeks after completion of the second dose are expected in the coming months and will be submitted to the FDA to support a potential expansion of this requested [authorization],' the company wrote in a statement.