Pfizer (PFE  ) and BioNTech (BNTX  ) asked the U.S. Food and Drug Administration (FDA) earlier this week to authorize a third dose of its COVID vaccine for children between the ages of 5- to 11-years old to act as a booster against Omicron.

The submission on Tuesday followed data Pfizer released earlier this month which demonstrated a strong immune response in this age group after receiving a booster dose about 6 months after their primary two-dose series. The 10-microgram booster dose--which is the same level given to children and preteens in their initial series--also did not produce any new safety concerns based on the trial, according to Pfizer.

The companies also plan to submit data to the European Medicines Agency (EMA) and other global health regulators for booster shot authorization in the coming weeks, according to Pfizer.

Studies have demonstrated that the protection provided by COVID vaccines against infection diminishes over time. Moreover, Pfizer's approved COVID vaccine was developed to protect against the orignal SARS-CoV-2 virus, meaning it offers less protection against highly mutated strains including Omicron, as they have adapted to evade the antibodies produced by the vaccine. However, the vaccine still provides high levels of protection against severe infection, hospitalization, and death.

Back in January, the FDA authorized Pfizer booster shots for young adolescents between the ages of 12- to 15-years-old in response to the then-new Omicron varant spreading rapidly in the United States. That approval was made without first consulting the agency's vaccine advisory committee for a recommendation. It is unclear if the FDA will seek a committee recommendation for this booster shot.

Pfizer is also seeking FDA authorization for its three-dose vaccine program for children under 5-years-old. Currently, this age group is the only one that is not eligible for COVID vaccination in the U.S.