The Trump administration’s cuts to the largest global H.I.V. program last year resulted in sharp drops in both prevention efforts and treatment for the people most at risk from the disease, according to the first large survey of organizations that had received the funds.

The findings show a grimmer picture of the impact of the cuts than the State Department’s data, released in April, which seemed to suggest that the program had helped to treat about as many people last year as it had in 2024.

To comply with the administration’s policies, the new survey, conducted by the H.I.V. charity amfAR, found, three-quarters of the organizations stopped providing services to those at highest risk from H.I.V. — sex workers, men who have sex with men, transgender people and people who inject drugs. The results are scheduled to be presented next week at a large international AIDS conference in Rio de Janeiro.

A second study, conducted by a multinational group of scientists, which will also be presented at the conference, found that the cuts had disproportionately affected children with H.I.V. The program, called the President’s Emergency Plan for AIDS Relief, or PEPFAR, supported treatment for about 77,000 fewer children in 2025 than it had the previous year, representing a 14 percent decline, the study found.

“We have not verified this specific report, but we can categorically say that its methodology is flawed,” the State Department, which oversees PEPFAR, said in an emailed statement, “The Trump Administration has strengthened PEPFAR through clear strategic direction, promoting greater recipient-country ownership, and sharpening the program’s focus on measurable health outcomes.”

Worldwide, nearly half of all children living with H.I.V. do not have access to treatment, according to UNAIDS, the United Nations program.

President George W. Bush started PEPFAR in January 2003, when H.I.V. medications were still unavailable in many parts of the world. The program is credited with saving 26 million lives, across more than 50 countries, making it the most successful endeavor of its kind.

But last year the Trump administration reshaped the program, saying the low-income nations that benefited must take on more of the costs of treating and preventing H.I.V. among their own citizens.

“We unfortunately are going through a very complex and difficult moment, where all these good achievements are challenged by the new policies,” Dr. Beatriz Grinsztejn, president of the International AIDS Society, said at a press briefing last week.

It is too early to gauge the impact of the cuts on H.I.V. rates, and it may continue to be challenging because many data collection programs have been scaled back or shut down as a result of the U.S. aid cuts.

In the first study, researchers collected information from 166 organizations, about one-quarter of the total funded by PEPFAR, in 46 countries. Delayed or terminated awards in 2025 caused these groups to shut down at least 1,700 sites that had delivered H.I.V. services, and to lay off more than 16,000 workers, the survey found.

Just six organizations accounted for 85 percent of the site closures, an indication of how the loss of funding to a single recipient can shutter hundreds of service points at once, the researchers said.

Sites that stayed open also felt the effects of the cuts.

“Even if a site doesn’t close, what you’re seeing is longer wait times, and fewer staff, and nonfunctioning data systems,” said Jennifer Sherwood, amfAR’s director of research and public policy.

The disruptions hit local organizations the hardest, contrary to the administration’s stated goal of empowering such groups and helping them move away from multinational aid organizations, she said.

After an initial freeze on all PEPFAR funds early in 2025, the administration allowed treatment to continue, but limited funds for prevention mostly to programs to stop transmission of H.I.V. from pregnant and breastfeeding women to their children.

In January, the administration also expanded the so-called Mexico City Policy, forbidding organizations that receive U.S. funds from providing most services related to gender, diversity, and reproductive health. More than 60 percent of organizations stopped providing at least one service and 44 percent stopped serving specific populations, the amfAR survey found.

Some organizations were required to revise their materials and strip out words that pertained to specific topics, and some of those changes altered the larger meaning. For example, in one case, “sex work” was revised to read “sex trafficking,” a term “which describes something entirely different,” noted Elise Lankiewicz, a policy associate at amfAR.

In some cases, the changes had nothing at all to do with prohibited concepts, and flagged phrases like “transfer of knowledge,” perhaps because it contained the fragment “trans.”

About half of the organizations surveyed also reported disruptions in their supply chains, including difficulty procuring condoms, lab supplies and antiretroviral drugs for treatment.

“For better or worse, PEPFAR ended up being a really interconnected system,” Ms. Lankiewicz said. “Trying to carve out and cancel certain awards had ripple impacts throughout the whole program.”

The system that is left “is really a treatment-heavy model, which isn’t really conducive to controlling the H.I.V. epidemic long-term,” she added.

But some evidence suggests the cuts have also affected treatment. In a separate analysis published last month in the journal Nature Health, Ramona Godbole, a senior manager at the Clinton Health Access Initiative, and other researchers reported a 10 percent decrease in the number of people treated with support from PEPFAR.

In the new study to be presented next week, the same researchers focused on PEPFAR support for children living with H.I.V., because they “can get very sick very quickly without access to drugs, and so the stakes are really high,” Ms. Godbole said.

The State Department said its policies have reduced the number of children becoming infected in the first place. “The number of children testing positive and on treatment for H.I.V. has continued to decline,” the department said in its statement.

The number of children receiving treatment for H.I.V. has slowly been decreasing in recent years because of the success of efforts to prevent babies from being born with the virus. But the 14.2 percent decline last year was a bigger drop than has been seen before, she said. India and South Africa each reported a decline of more than 45 percent.

“It’s a signal, not a verdict,” Ms. Godbole said. “But it’s certainly the signal to do more investigation.”