(CNN) — The US Food and Drug Administration is expected to broaden eligibility for Pfizer Covid-19 vaccine boosters to youths ages 12 to 15 in the coming days, according to a person familiar with the agency’s plan.

People as young as 16 are already eligible to receive boosters of the Pfizer vaccine six months after their two-dose series. Youths ages 12 to 15 have been eligible to receive the Pfizer Covid-19 vaccine since May; as of early July, about 4 million people in this age group had been fully vaccinated and would be eligible for a booster immediately.

When asked on Wednesday about boosters for adolescents and younger teens, US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky told CNN that the FDA “is looking at that right now. Of course the CDC will swiftly follow as soon as we hear from them and I’m hoping to have that in … the days to weeks ahead.”

US health officials have been pushing for months for adults to get boosted, especially after the emergence of the Omicron variant.

Studies have shown that the two-dose Pfizer and BioNTech vaccine does not provide sufficient protection against infection with Omicron, although it still appears to help protect against severe disease. A booster dose increased protection significantly, studies have shown.

The latest timeline for people ages 12 to 15 was first reported by The New York Times. The Times also reported that the booster schedule will shift from six months after the primary dose series to five months, and a booster shot is expected to be authorized for children ages 5 to 11 with immune deficiencies.

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