International researchers say it's not time yet for healthy, vaccinated adults to get COVID-19 booster shots, but the Biden administration wants to make them available on Sept. 20.

President Biden has said that the decision of which booster shots to give, when to start them, and who will give them, will be left completely to the scientists at the FDA and the Centers for Disease Control and Prevention.

It initially called for all Americans to be eligible for boosters eight months after their final dose.

Dr. Perry Wilson, a physician with Yale Medicine, says it “doesn't look like that's going to happen.”

“They're seeing a fair amount of pushback both from CDC and potentially from the FDA,” he said.

He said the data does show efficacy from the COVID-19 vaccines drops over time.

"Efficacy at preventing symptomatic disease has waned a little bit, depending on your age group might be down to 80% or so,” said Dr. Wilson.

But a report published in the Lancet journal on Monday found that the shots are still working, and it's not time for a booster yet.

"Even now, even in the face of Delta, even in people who are fairly far out from their initial vaccination, the vaccines remain highly effective against serious illness, hospitalization and death from COVID-19,” said Dr. Wilson.

Dr. Wilson said getting all Americans their first shot is more important than thinking about getting some of them a third. He does expect the FDA and CDC to recommend boosters for those with compromised immune systems and likely for seniors.

"Maybe people above age 65, at least for people above age 75. Because the data really does show immunity might be waning in that population,” he said.

The FDA and CDC are expected to advise the White House about who should be eligible for COVID-19 boosters and when sometime this week.