The new study, published in The Lancet and simultaneously presented at the 2025 Conference on Retroviruses and Opportunistic Infections (CROI) on Tuesday, is the first to evaluate a once-yearly injection of an HIV pre-exposure prophylaxis (PrEP) medication.

PrEP is a medication regimen used to prevent HIV infection in people who are at risk of exposure to HIV by blocking the virus from entering and replicating in human cells. PrEP is currently approved as a daily pill or an every-other-month injection.

When taken correctly, PrEP is more than 90% effective at preventing HIV. However, in 2023 only 3.5 million of the 21.2 million people who would benefit from PrEP were receiving it, highlighting the need to eliminate existing barriers – such as stigma and discrimination, limited access to health clinics, lack of adherence to currently available regimens, and medication cost – including via longer-acting PrEP options.

To be sure, PrEP medications are not the same as vaccines and there is currently no available vaccine to prevent HIV.

HIV remains a major public health concern, with 1·3 million new infections globally in 2023, according to the global HIV & AIDS statistics fact-sheet 2024.

In the new study, 40 participants without HIV aged 18–55 years were injected with one of two lenacapavir formulations administered as a single dose.

Lenacapavir was first developed as an antiretroviral medication used to treat HIV (in combination with other HIV medications). It is a novel, first-in-class, long-acting multistage HIV-1 capsid inhibitor currently being developed for PrEP.

The study took place at two clinical research centres in the USA. Samples were collected at prespecified timepoints up to 56 weeks to evaluate the safety and pharmacokinetics (how a medication moves through the human body) of the injection. The medication was generally well tolerated, with injection site pain being the most common adverse event. No clinically significant safety concerns were identified, said the researchers.

“After 56 weeks, medium plasma concentrations of intramuscular lenacapavir exceeded those associated with efficacy in phase 3 studies of a twice-a-year subcutaneous injection (an injection underneath the skin and above the muscle tissue) of lenacapavir for PrEP,” read the paper.

“As a phase 1 study, the trial measured safety and the body’s physiological response – it did not measure effectiveness at preventing HIV infection, and further clinical trials are needed, including with participants from more diverse population sets,” it added.

The authors added that expanding options for PrEP, such as a potential once-a-year injection, can help overcome current barriers to access and adherence and drive progress toward reducing new HIV infections.

Health experts said it can be a good prevention tool.

“This can be a good prevention tool for vulnerable population if the results come out well in subsequent trials. AS of now the results seem promising, no doubt, but we need to larger studies over a period of time as these are prevention trials and if a young high-risk patient is taking this drug, how long can it be safely taken, and if a person develops some co-morbid condition later on then can this drug be taken with other drugs meant to be taken on a long-term basis. But for now, it will have benefits over the current regimen that needs to be taken regularly,” said Dr R Gangakhedkar, former head of epidemiology, ICMR.