Pfizer and BioNTech reported Friday that studies show children aged between 2 those younger than 5 did not produce an adequate response to its COVID-19 vaccine for young children and that it will begin administering a third dose to those trial participants as studies continue.

In a press release, Pfizer noted that the dose for young children, which is one-tenth the strength of its vaccine for people aged 16 and up, provided the same amount of protection the adult vaccine provides to people aged 16 to 25. However, children aged between 2 and 4 did not produce an adequate response.

"Compared to the 16- to 25-year-old population in which high efficacy was demonstrated, non-inferiority was met for the 6- to 24-month-old population but not for the 2- to under 5-year-old population in this analysis," Pfizer's press release said.

The third shot for children aged 2 to 4 will be administered at least two months after the final shot.

The company added that trials so far had not produced any safety concerns. They noted that the trial studies would remain double-blinded when adding a third dose.

Pfizer made the announcement Friday, the same day that it announced it would be seeking full authorization for the use of its COVID-19 vaccine in adolescents as young as 12.

Pfizer's vaccine is fully approved for people as young as 16, and available through emergency use authorization for kids as young as 5.