US funding cuts to South Africa have dismantled HIV prevention programmes just as they are needed to support the roll-out of the new prevention drug lenacapavir, a report said on Tuesday.

South Africa has the world's largest population of HIV-infected people, with about 8-million - one in five adults - living with the virus. The US funded about 17% of the country's HIV budget until President Donald Trump slashed aid last year as part of his "America First" foreign policy.

The report by Physicians for Human Rights, a US-based NGO, said that Washington effectively wasted billions of dollars of investment by abandoning research infrastructure and health delivery platforms which it had spent years building in South Africa.

In the near term, that will hinder the rollout of lenacapavir, a twice-yearly injectable HIV prevention drug which arrived in South Africa this month, the report said.

"We have a product that's really powerful, but we don't have a programme to fit it into anymore," said Emily Bass, a co-author of the report.

The US had funded community-based outreach and peer education programmes about different HIV prevention options, for example, without which they may not know lenacapavir exists, she said. 

South Africa's health department and the US State Department did not immediately respond to requests for comment.

The impact of the funding cuts is difficult to measure because funding for data collection was also cut, said the report. However, it documented widespread disruption to HIV programmes in both clinics and communities, based on interviews with dozens of people involved in South Africa's HIV response.

"We know that there are many LGBTQI communities, many sex workers, many, many young people who are not accessing services because of this," said Yvette Raphael, executive director of Advocates for the Prevention of HIV in South Africa.   

Last week, US government figures suggested HIV aid globally had been maintained despite the cuts; but the data showed declines in testing and diagnoses.