Pfizer asked U.S. regulators Monday to expand use of its updated COVID-19 booster shot to children ages 5 to 11.

Elementary school-aged children already received kid-sized doses of Pfizer's original vaccine, a third of the dose given to everyone 12 and older -- two primary shots plus a booster.

If the Food and Drug Administration agrees, they would start getting a kid-sized dose of the new omicron-targeted formula when it was time for their booster.

FDA vaccine chief Dr. Peter Marks said last week he expected a decision on boosters for that age group soon.

Pfizer and its partner BioNTech also announced a new study of the omicron-focused booster in even younger children, those ages 6 months through 4 years, to test different doses.

Updated boosters made by both Pfizer and rival Moderna rolled out earlier this month for everyone 12 and older. They're a tweak to vaccines that already have saved millions of lives -- a combination or "bivalent" shot that contains half the original recipe and half protection against the BA.4 and BA.5 omicron relatives responsible for most of today's COVID-19 cases.

The hope is that the modified boosters will help tamp down continuing COVID-19 cases and blunt another winter surge. As of last week, the Centers for Disease Control and Prevention said 4.4 million Americans had gotten an updated booster so far.

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