Soon after Biden made the comments—at an Oval Office meeting with Israeli Prime Minister Naftali Bennett on Friday—a White House official said there had been no change in the plan to administer boosters after eight months.

Biden nonetheless said he talked with infectious disease expert Anthony Fauci about the possible timeline change earlier in the day, signaling his interest in studying the issue.

Biden told Bennett that he’s “considering your advice that we should start earlier” in administering boosters in the face of the Delta variant, he said. One of the questions, Biden said, is: “Should it be five months?”

Relying substantially on data from Israel, Biden’s senior health team announced a plan this month for any adult to get a booster, beginning Sept. 20, if it’s been eight months since their second shot of either the Pfizer Inc.-BioNTech SE or Moderna Inc. vaccines. That plan is still subject to authorization by the Food and Drug Administration.

The Biden administration cited warning signs that vaccine efficacy is waning over time, and that the shots aren’t as effective against the Delta variant. The variant is highly contageous and fueling an increase in coronavirus cases around the country.

But some health experts say it’s not yet clear if boosters are needed for all adults, including the young and healthy. 

The White House official, speaking on condition of anonymity, said administration health and medical experts continue to review a range of data. The virus is unpredictable and the administration is planning for every scenario, the official said. 

Moderna spokesman Ray Jordan said “we have been in regular dialogue with the FDA on this topic,” and that the company expects to have additional data “within a few weeks.”

Pfizer didn’t immediately respond to a request for comment. 

The other vaccine in use in the U.S.—a one-shot vaccine from Johnson & Johnson—was authorized in February and it’s not yet clear what U.S. regulators will recommend for boosters. J&J spokesman Jake Sargent said Friday that the company is working with the FDA and other agencies “regarding boosting with the Johnson & Johnson COVID-19 vaccine.”

—With assistance from Riley Griffin