Federal officials have secured enough doses to cover a fourth shot for Americans age 65 and older as well as the initial regimen for children under age 5, should regulators determine those shots are necessary, said three officials, speaking on the condition of anonymity to detail funding decisions. But the officials say they cannot place advance orders for additional vaccines for those in other age groups, unless lawmakers pass a stalled $15 billion funding package.

“Right now, we don’t have enough money for fourth doses, if they’re called for,” White House coronavirus coordinator Jeff Zients said on a forthcoming episode of “In The Bubble with Andy Slavitt,” which was recorded Monday and shared with The Washington Post. “We don’t have the funding, if we were to need a variant-specific vaccine in the future.”

Federal regulators and health officials have not yet determined whether a fourth shot is needed, and some experts question whether the extra dose will be necessary to boost protection for the general population.

But administration officials said placing orders for additional doses ahead of time — rather than waiting for the United States to be swamped with another wave of the virus — was imperative and a key lesson from the pandemic’s past two years. They also noted that the fast-moving omicron variant evaded some immune protection conferred by existing vaccines, demonstrating the need to invest in more targeted shots that could better fend off omicron and potential future variants.