Federal officials told state governors that as of earlier this week up to 53 million doses were still waiting to be ordered by the states – a staggering amount that, depending upon the type of vaccine, would offer protection against the virus to some 25 million people.
That federal surplus is in addition to an unknown number of vaccine doses waiting for arms at vaccination sites and pharmacies in states like Wyoming, Idaho, Mississippi, Louisiana and Alabama that have the lowest vaccination rates.
“We are right now in possession of a supply that could be shared, that we're worried about expiring,” Arkansas GOP Gov. Asa Hutchinson told the White House in phone call on Tuesday with other governors. Audio of the private call was obtained by ABC News.
The Biden administration insists that the number of wasted doses in the U.S. is extremely low and that the vast majority of supply is not at risk of expiring. But the idea of a growing vaccine surplus is a new dilemma for the White House, which took control when supply was scarce and the federal government still hadn’t purchased enough vaccine for every American. Now, with nearly 60 percent of eligible Americans having one shot, the pace of those shots has been cut in half in the past six weeks to 1.7 million a day.
Meanwhile, global outbreaks have prompted concerns of new mutations of the virus that could chip away at the effectiveness of vaccines and leave vaccinated Americans at risk.
"We are going to have this embarrassing accumulation of surplus," said Stephen Morrison, director of the Global Health Policy Center at the Center for Strategic and International Studies.
Morrison, who predicted as many as 30 percent of Americans will refuse the vaccine entirely, said the primary concern for the Biden team will be ensuring any U.S. recovery is "durable" before diverting supply.
"At the same time, we have this wildfire raging beyond our borders that they will have to address or else it will come back and bite us," he said.
The Biden administration has pledged $4 billion to Covax, the global vaccine effort, and promised to donate 20 million doses of the vaccines currently available in the U.S. by the end of June – a fraction of the 800 million the U.S. says it is buying from Pfizer, Moderna and Johnson & Johnson. The administration also plans to export 60 million doses of AstraZeneca, a vaccine used overseas but not cleared yet by U.S. regulators.
When asked about the surplus, Andy Slavitt, a top adviser to the president on the COVID-19 federal response, said the administration is working to "more tightly manage the supply" of vaccines. But he signaled the primary focus for now will remain on immunizing every American using mobile clinics and vaccinating people at malls and schools.
The U.S. also will need much of the vaccine it’s planning to buy to develop booster shots and to immunize children ages 11 and younger once they become eligible.
The "first objective and prime hope," Slavitt told reporters Tuesday, is "that people in this country use the doses that we have all procured and that … clearly (is) our path to better health and to getting back to normal."
If Americans hold out though, questions on what to do with U.S. vaccine riches are likely to grow louder.
The head of the World Health Organization, Tedros Adhanom Ghebreyesus, this month called the global imbalance the “unfolding of a moral catastrophe” and implored wealthy countries to donate doses instead of vaccinating its children and teens because they are at relatively lower risk.
Arthur Caplan, who runs a vaccine ethics and policy program at NYU's Grossman School of Medicine, said it's not wrong for a country to vaccinate its own residents before going abroad. The U.S. can’t help others if it’s still mired in a pandemic, and preventing adolescents from spreading the virus makes sense, he said.
Complicating matters too is that the international vaccine program Covax has stumbled, relying too heavily on India – a nation now consumed with its own COVID outbreaks -- to produce vaccines for the world.
"It isn’t enough to issue pronouncements from Geneva, saying 'Send us all your vaccines and we’ll distribute,'" he said. "I want to hear: What are the rules? Who are you prioritizing? And how are you going to enforce it?"
But Caplan agrees a growing U.S. surplus presents a challenge. He predicts American businesses and schools will eventually impose mandates once the vaccines are given full licensure by federal regulators.
"The worst thing we can do is not find people to take vaccines before they expire," Caplan said.
For their part, governors are still trying to entice their residents to get a vaccine in ways almost uniquely American: high-dollar sweepstakes, college scholarships, game tickets and other swag.
In Maine, Democratic Gov. Janet Mills sought to boost vaccinations and the state’s brand at the same time by offering fishing and hunting licenses, tickets to local sports games and gift cards to L.L. Bean, the state’s flagship store. North Carolina offered $25 “summer cash cards” to people who got their first dose, as well as people who drove them there.
But even those efforts appear to be stalling out, and governors may need to up the ante as time goes by.
New York Gov. Andrew Cuomo suggested the federal government could pay for a $100 tax credit for anyone who can prove they are vaccinated.
“The higher we get up the hill, the steeper the going,” Cuomo told the White House.
ABC News' Cheyenne Haslett and Brian Hartman contributed to this report.