Pfizer Inc. asked U.S. regulators for emergency-use authorization of a booster shot of its COVID-19 vaccine in children ages 5 to 11, setting in motion an effort to provide extra protection to kids.

Pfizer and partner BioNTech SE submitted data to the U.S. Food and Drug Administration from a late-stage study that showed a third-dose booster shot, given about 6 months after the second dose, provided a strong immune response.

The companies also plan to submit data to the European Medicines Agency and other regulators around the world, according to a statement Tuesday. No new safety concerns were identified, they said.

The U.S. campaign to immunize children has tapered off, with 28% of children ages 5 to 11 fully vaccinated, according to the Centers for Disease Control and Prevention. Fewer than a quarter of adolescents ages 12 to 17, who are already eligible for boosters, have received one. That bodes poorly for a booster campaign among the youngest children.

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