WASHINGTON (AP) — The Biden administration’s embattled plan to dispense COVID-19 booster shots to most Americans faced its first major hurdle Friday as a government advisory panel met to decide whether to endorse extra doses of the Pfizer vaccine.

The FDA experts were scheduled to vote on one basic question: Does the evidence show that a Pfizer booster would be safe and effective for people 16 and older?

The CDC has said it is considering boosters for older people, nursing home residents and front-line health care workers, rather than all adults.

While the Biden administration has said that its priority is to get people vaccinated in the first place, the deepening crisis has given urgency to efforts to shore up Americans’ protection against the virus by giving them booster shots.

Israel already is offering boosters to its citizens, and Britain this week announced plans to start giving them to people over 50 and certain other vulnerable groups once they are six months past their second dose.

Sharon Alroy-Preis of Israel’s Ministry of Health said the booster dose improves protection tenfold against infection in people 60 and older.

A Pfizer study of 44,000 people showed effectiveness against symptomatic COVID-19 was 96% two months after the second dose, but had dropped to 84% by around six months.

A company study found that giving a booster to about 300 people six months after their second dose bumped levels of key virus-fighting antibodies higher than the earlier shots -- and more important, they were strong enough to handle the delta variant and another worrisome strain.

It said boosters would be dispensed eight months after the second dose of the Pfizer and Moderna vaccines.

has already approved Pfizer and Moderna boosters for certain people with weakened immune systems, such as cancer patients and transplant recipients.