As the reality sets in that the United States is drastically diminishing its foreign assistance to developing countries, an urgent conversation is starting among governments, philanthropists, and global health and development organizations.

It is centered on one crucial question: Who will fill this gap?

Last year, the United States contributed about $12 billion to global health, money that has funded treatment of H.I.V. and prevention of new infections; children’s vaccines against polio, measles and pneumonia; clean water for refugees; and tests and medications for malaria.

The next largest funder is the Gates Foundation, which disburses a fraction of that amount: its global health division had a budget of $1.86 billion in 2023.

“The gap that has been filled by the U.S. cannot be easily matched by anybody,” said Dr. Ntobeko Ntusi, the chief executive of the South African Medical Research Council.

U.S. assistance has been channeled through the United States Agency for International Development, or U.S.A.I.D., which the new Trump administration has largely dismantled, and other government agencies, including the National Institutes of Health, which is also facing substantial cuts in health research grants.

Many people are suggesting that other countries, particularly China, could move into some of the areas vacated by the United States, Dr. Ntusi said. Others are making urgent appeals to big philanthropies including the Gates Foundation and Open Philanthropy.

This conversation is most consequential in Africa. About 85 percent of U.S. spending on global health went to programs in or for African countries.

For countries such as Somalia, where U.S. aid made up 25 percent of the government’s whole budget, or Tanzania, where the U.S. funded a majority of public health care, the loss is catastrophic. And for the major global health agencies, the situation is similarly critical.

President Trump has already pulled the U.S. out of the World Health Organization, which is now trying to make an initial budget cut of $500 million for 2026-27 to cope with the withdrawal of American funds.

“Most of our neighbors on the continent, they’ve been completely reliant on the U.S. to procure most of the lifesaving medications for endemic infections,” Dr. Ntusi said. “And I don’t see most of the governments overnight being able to have the resources to cope. And so I think there’s going to be devastating consequences on lives lost from Africans who will die of preventable infections”

The U.S. is the largest donor to Gavi, an organization that supplies essential vaccines to the world’s poorest countries, and to the Global Fund to Fight AIDS, Tuberculosis and Malaria. The U.S. contribution is required by Congress. Asked about the commitment to these and other multilateral agencies including the Pandemic Fund, a State Department spokesperson said that the programs were being reviewed to see if they aligned with the national interest, and that funding would continue only for those that met this condition.

Who Steps In?

There is no indication that additional funding will come from the other G7 countries, the European Union or other high-income nations. Britain, Germany, France, the Netherlands and Scandinavian countries have all reduced their foreign aid. Some new donor countries have come forward to support the W.H.O., including Saudi Arabia and South Korea, but their spending is dwarfed by the amount the U.S. once gave.

Of nongovernmental players, the World Bank is best placed to provide long-term support for health spending. The bank has said little so far. It could offer countries hit hard by the U.S. cutoff innovative financing such as debt-for-health-care swaps to give nations struggling under heavy debt burdens some fiscal freedom to make up lost health care funding. However, the U.S. is the largest shareholder of the bank, and the Trump administration would have influence over any such investment.

Much of the public discussion about filling the vacuum left by the U.S. has focused on China, which has built a significant presence by financing infrastructure projects in African countries, particularly those with extensive mineral reserves or strategic ports.

“There is good reason for them to do so,” said Ja Ian Chong, an associate professor of political science at the National University of Singapore. China regards foreign aid as a soft-power tool in its superpower rivalry with the United States, much as the United States did when setting up U.S.A.I.D. during the height of the Cold War with the Soviet Union. China seeks to use aid to garner more support from developing countries in the United Nations.

While Chinese aid has largely come in loans to build infrastructure, it includes support for more varied projects. China’s answer to Western development aid, a program unveiled in 2021 called the Global Development Initiative, includes $2 billion for upgrading livestock production in Ethiopia, fighting malaria in Gambia and planting trees in Mongolia, among other projects.

Mr. Chong said China’s ability to fill the opening left by U.S.A.I.D. could be constrained by its own financial limitations. China’s economy has stagnated because of a property crisis and rising government debt, and the country has already scaled back on big infrastructure loans.

To date, China has shown little interest in supporting global health programs, or in providing grants on a scale anywhere near U.S.A.I.D. levels. AidData, a university research lab at William & Mary in Virginia, estimates that Beijing provides about $6.8 billion a year in grants and low-cost loans.

Philanthropies

Philanthropies that were already working in global health have been deluged with panicked calls from organizations with frozen funds.

“I have talked to some foundations who have all said we’re being inundated with people saying, ‘Help us, help us, help us,’ and I think they’re trying to patch little holes,” said Sheila Davis, the chief executive of the nonprofit Partners in Health, which works with local governments to bring health care to communities in developing countries. But if a patchwork bailout can cover just 20 percent of what the U.S. was paying for, what should a new donor save? she asked. “Do you choose to save one program fully and then let others go? Or what is the best strategy?”

Chief among the foundations fielding pleas for help is the Gates Foundation, which has been warning its grant recipients that it cannot make up the gap. In addition to funding global health programs, the foundation also supports health research and is a major contributor to Gavi.

“There is no foundation — or group of foundations — that can provide the funding, work force capacity, expertise, or leadership that the United States has historically provided to combat and control deadly diseases and address hunger and poverty around the world,” the foundation’s North America director, Rob Nabors, said by email.

Multiple recipients of Gates Foundation funding, who declined to speak on the record because they were describing confidential conversations, said they had been told by foundation staff members that it would continue to fund research and programs in the areas it already worked, but wouldn’t expand significantly, and that while some grants might be restructured to try to compensate for part of the lost U.S. funding, the foundation’s work would continue to be “catalytic” rather than support large-scale programming like U.S.A.I.D. did.

John-Arne Røttingen, the chief executive of the Wellcome Trust, which is among the largest donors to global health research, said in an email that the foundation was “exploring what options might exist” in the new landscape. But, he said, its help would be “a drop in the ocean compared to what governments across the world need to provide.”

A couple of small organizations, such as Founders Pledge, have started “bridge funds,” ranging from about $20 million to $200 million, to try to help plug immediate gaps.

But the philanthropic sector has largely been silent about the momentous change in the landscape. Major players that have already put hundreds of millions of dollars into health care in Africa, such as the Susan T. Buffett Foundation, did not respond to questions about their plans. The Delta Foundation (co-founded by the Zimbabwean telecom billionaire Strive Masiyiwa) declined to discuss the issue.

Two executives at smaller private foundations said there was a reluctance to say anything publicly because of fear of retribution from the Trump administration, including a potential loss of charitable status.

African Governments

African governments are under tremendous pressure from frustrated citizens to assume responsibility for the health spending that was coming from the U.S. The issue led the agenda at a meeting of the continent’s health ministers at an African Union summit last week.

In the 24 years since the Union adopted what’s called the Abuja Declaration, committing its 42 members to spending 15 percent of their budgets on health, only a couple of states have ever hit that target, and for a year or two at most. Average health spending by African countries is less than half that amount.

In Nigeria, the president convened an emergency cabinet committee to make a plan for the budget shortfall, and Parliament allotted an extra $200 million to the national budget last week. But that extraordinary measure illustrates the scale of what’s been lost: it’s less than half of the $512 million that the U.S. gave Nigeria for health care in 2023.

Nigeria’s health minister, Dr. Muhammad Pate, said that nearly 28,000 health care workers in the country had been paid in whole or part by U.S.A.I.D., which also covered three-quarters of the bill for drugs and test kits for the 1.3 million Nigerians who live with H.I.V.

Nigeria will quickly need to find new ways of operating, he said, including boosting manufacturing of some of those items domestically. “It may not be as fancy, but at least it will serve,” Dr. Pate said.

He also predicted that the end of U.S. aid would accelerate what he called a “realignment” in Africa. “The world has shifted in the last 20 years,” he said. “So we have other actors: We have China, India, Brazil, Mexico and others.”

Deisy Ventura, a professor of global health ethics at the University of São Paulo, said the change could open opportunities for other countries to exert newfound influence.

“The retreat of the United States may open space for new leaders now,” she said. “It’s important for us in the global south to imagine an international coordination of emergency preparedness and response without the United States.”

Berry Wang contributed reporting from Hong Kong.