In April, the Biden administration announced plans to share millions of Covid-19 vaccine doses with the world by the end of June. Five weeks later, nations around the globe are still waiting to learn where the vaccines will go and how they will be distributed.
To President Joe Biden, the doses are not only the ultimate carrot for America's partners abroad, but also a necessary tool for global health, capable of saving millions of lives and returning a semblance of normalcy to friends and foes alike.
The question is, what share of doses should be provided to those who need it most, and how many should be reserved for US partners?
So far, the answer appears to be that the administration will provide the bulk of the doses to Covax, the UN-backed global vaccine sharing programme meant to meet the needs of lower income countries.
While the percentage is not yet finalised, it would mark a substantial – and immediate – boost to the lagging Covax effort, which to date has shared only 76 million doses with needy countries.
The Biden administration is considering reserving about a fourth of the doses for the US to dispense directly to individual nations of its choice.
The growing US stockpile of Covid-19 vaccines is seen not only as a testament to American ingenuity, but also its global privilege.
More than 50 per cent of Americans have received at least one dose of the vaccine, and more than 135 million are fully vaccinated, helping to bring the rate of cases and deaths in the US to the lowest level since the earliest days of the pandemic.
Scores of countries have requested doses from the US, but to date only Mexico and Canada have received a combined 4.5 million doses.
The US also plans to share enough doses with South Korea to vaccinate its 550,000 troops who serve alongside American service members on the peninsula.
The broader US sharing plan is still being finalised, a White House official said, having been the subject of policy debate inside the White House and across the federal government, and also involving Covax and other outside stakeholders such as drug manufacturers and logistics experts.
“Our nation’s going to be the arsenal of vaccines for the rest of the world,” Mr Biden said on May 17, when he announced the US pledge to share more doses.
He added that, compared to other countries like Russia and China that have sought to leverage their domestically produced doses, "we will not use our vaccines to secure favours from other countries".
Still, the partnership with the South Korean military points to the ability of the US to use its vaccine stockpile to benefit some of its better-off allies.
It was not clear whether South Korea would pay for its doses from the US. Most of the other doses were expected to be donated.
Samantha Power, the new USAid administrator, provided the first indication of the likely allocation last week in testimony to the Senate.
She told the Senate Appropriations Committee that “75 per cent of the doses we share will likely be shared through Covax. Twenty-five per cent of whatever our excess supply is that we are donating will be reserved to be able to deploy bilaterally.”
Administration officials cautioned that Mr Biden had not yet signed off on the precise split and that it could still change. One said the administration would be working in coming days to synchronise its supplies with the global vaccine-sharing organisations.
Mr Biden has committed to providing other nations with all 60 million domestically produced doses of the AstraZeneca vaccine.
That vaccine has yet to be authorised for use in the US but is widely approved around the world. The US-produced doses will be available to ship as soon as they clear a safety review by the Food and Drug Administration.
The president has also promised to share 20 million doses from existing production of Pfizer, Moderna and Johnson & Johnson vaccine stocks. Even more doses are expected to be made available to share in the months ahead.
As part of its purchase agreements with drug manufacturers, the US controlled the initial production by its domestic manufacturers. Pfizer and Moderna are only now starting to export vaccines produced in the US to overseas customers. The US has hundreds of millions more doses on order, both of authorised and in-development vaccines.
"It's obviously challenging because so many countries face this need right now," Ms Power said, calling the decision of where to send doses "an urgent question".
She said it hinged on a combination of "the relationship we have with the countries, the public health and epidemiological scientific trajectory of the disease, and a sense of where the vaccines can do the most good, the infrastructure and readiness of countries to receive vaccines".
The US has pledged $4 billion to Covax to help it procure and distribute vaccines. Covax has committed to sharing the doses with more than 90 countries, including many with which the US has tumultuous relations.
Leaving it to Covax to decide how the bulk of the US-provided doses are distributed is seen by the administration as the most equitable way to determine who will benefit. That could allow the US to avoid any political fallout that might come from sharing the vaccine directly with adversaries.
“It’s not only a symbol of American values – it’s smart global health policy,” said Tom Hart, acting CEO of the ONE Campaign, which has pressed the Biden administration to move faster to develop its global sharing plan.
"I don't want a variant cooking up in some remote part of the world, anywhere in the world, which then might get around the current vaccines that we've got."
Globally, more than 3.5 million people are confirmed to have died from the coronavirus. The US has seen the largest confirmed loss of life from Covid-19, with more than 594,000 deaths.