(Reuters] -Pfizer, Inc. and BioNTech Se (NASDAQ) announced on Tuesday they had applied to the U.S. regulator for authorization for a booster of their COVID-19 vaccination for children aged between 5 and 11 years.

Companies earlier in October reported on data from a late-stage study that showed that a third dose was more effective against both the Omicron variant and coronavirus versions among the children.

Uncertain how many people are looking for another dose of the vaccine in that age group. Data from the U.S. Centers for Disease Control and Prevention show that only 28 percent of children 5-11 years are currently fully vaccinated. This is approximately 8.2 million.

Some people are skeptical about the necessity of boosters for younger children, given the lower risk of serious infection and hospitalization.

Pfizer BioNTech (NYSE: ) has filed to allow the approval of a 10-microgram booster for children 5-12 years old. The vaccine is also available for adults in a 30 microgram dosage.

For children aged five to eleven years, October saw the approval of two doses of primary COVID-19 from BioNTech and Pfizer.

In January the U.S. Food and Drug Administration (FDA), approved the use of a third dosage of COVID-19 vaccine to be administered to children between 12 and 15. Children aged between 5-11 years and immunocompromised have been authorized to receive a booster shot by the agency.

Rival Moderna (NASDAQ) Inc awaits a U.S. regulator’s decision regarding the primary COVID-19 series being used among age groups younger than 18 years.

The company plans to apply to FDA to authorize its COVID-19 vaccine for children aged six to five years, by April end.