The US foreign assistance freeze is causing widespread disruption in the global AIDS response, amid confusion over the application of a waiver granted to such programmes, the United Nations said Friday.
"It is quite a systemic shock," Christine Stegling, deputy head of UNAIDS, told reporters in Geneva.
Shortly after taking office on January 20, Trump signed an executive order implementing a 90-day pause in US foreign development aid.
His administration later issued waivers for food and other humanitarian aid, as well as for funding for medication under PEPFAR, a major US programme battling HIV/AIDS.
"We're really grateful for that," Stegling said, pointing out that US foreign assistance covers 70 percent of the global AIDS response, and 50 percent of her agency's budget.
Two thirds of the 30 million people living with HIV in the world depend on US aid for their treatment, she pointed out.
The waiver means they "can continue their medication", she said.
"It's a huge number of people who depend on that support."
While the exemption was welcome, Stegling warned that "there is still a lot of confusion... about how the waiver will be implemented".
"We're seeing a lot of disruption of delivery of treatment services, especially at the community level," she said.
She highlighted that many community organisations and a number of governments were unclear on what would be covered, and were being "overly cautious" and halting programmes to avoid being asked to repay the funds.
"There is a real risk that services will not be open again."
In Ethiopia, for instance, she said 5,000 public health workers on contracts funded by US assistance "have been terminated", as had 10,000 data clerks tasked with monitoring and ensuring people are on treatment, Stegling said.
She cautioned that the global impact could be "treatment interruptions", and a failure to get more people onto treatment.
The main concern, she said, was "the long-term impact on prevention of new HIV infections".
Amid a push to prioritise the use of accessible funds governments and community organisations were likely to prioritise "keeping people on treatment rather than ... preventing new infections", she pointed out.
Stegling said UNAIDS was hoping that after a US review of its foreign aid funding, Washington would decide to continue with the large-scale backing it has provided for over three decades to the global AIDS response.
According to the UN agency modelling, a discontinuation of PEPFAR between 2025 and 2029 would lead to a "400-percent increase in AIDS deaths", or 6.3 million deaths, if no other funding was found, she said.