A twice-yearly injection called lenacapavir prevented every single HIV infection in a late-stage clinical trial involving more than 2,000 cisgender women in South Africa and Uganda — a result so striking that independent monitors halted the blinded phase early and offered the shot to all participants.
At a glance
- Lenacapavir injection: In the PURPOSE 1 trial, zero of 2,134 women who received the twice-yearly shot contracted HIV — a 100% efficacy rate across the study period.
- Daily PrEP comparison: Women in the same trial who took oral PrEP pills — either Truvada or Descovy — had infection rates of roughly 2%, consistent with other real-world studies of daily pills.
- HIV prevention trial scope: The double-blind, randomized study enrolled 5,300 cisgender women beginning in August 2021 C.E., with results announced by trial sponsor Gilead Sciences on June 20, 2024 C.E.
Why a shot changes everything about adherence
Daily oral PrEP — pre-exposure prophylaxis — has been the standard of care for HIV prevention since it was introduced over a decade ago. In controlled trials, pills like Truvada can be 99% effective. But in the real world, that number falls sharply.
One study found PrEP effectiveness as low as 26% in some populations. The reason is simple: people don’t always take their pills every day. In South Africa, researchers found that women faced social stigma around carrying the medication — a partner might assume they were HIV-positive, or suspect them of having multiple partners.
“It’s hard to take a medication every single day,” said Dr. Jason Zucker, an assistant professor of medicine and infectious disease expert at Columbia University Vagelos College of Physicians and Surgeons. “A medication that is given every six months has a lot of potential because, essentially, if you can make two visits a year, you are protected for an entire 12 months.”
Dr. Philip Grant, director of the HIV clinic at Stanford University School of Medicine, put it plainly: “It would be a big benefit in populations that have adherence challenges.”
The population this trial was built to reach
The decision to focus PURPOSE 1 on women in sub-Saharan Africa was grounded in data. Sub-Saharan Africa accounts for roughly 10% of the world’s population but holds two-thirds of all people living with HIV — approximately 25.7 million out of 38.4 million globally. Every week, around 4,000 teenage girls and young women on the continent are newly infected.
Lenacapavir is not a new molecule. The U.S. Food and Drug Administration approved it in 2022 C.E. as a treatment for multi-drug resistant HIV. PURPOSE 1 is the first trial to test it for prevention. An ongoing PURPOSE 2 trial is now analyzing its effectiveness in cisgender men, transgender men, transgender women, and non-binary individuals across Argentina, Brazil, Mexico, Peru, South Africa, Thailand, and the U.S.
The trial has not yet been peer-reviewed, and full publication in a scientific journal will be a key next step before regulators act on the data.
The cost barrier that could limit the breakthrough
The results have drawn wide enthusiasm, including from the People’s Medicines Alliance, a global coalition of more than 100 organizations across 33 countries. But advocates are also watching the price question with urgency.
Analysis presented at the 24th International AIDS Conference found that PrEP medications would need to cost less than $54 per patient per year for countries like South Africa to afford them at scale. Lenacapavir’s current price as an HIV treatment in the U.S. runs to $42,250 per new patient per year. Oral PrEP, by contrast, can cost less than $4 a month in some markets.
Activists in Uganda and South Africa have called on Gilead to license lenacapavir through the Medicines Patent Pool, a United Nations-backed body that partners with industry to enable generic manufacturing at lower cost. The concern is real: cabotegravir, a long-acting injectable PrEP approved in 2021 C.E., still may not reach Africa in generic form until 2027 C.E. due to regulatory timelines.
Gilead has stated its intention to “deliver lenacapavir swiftly, sustainably and in sufficient volumes, if approved, to high-incidence, resource-limited countries,” and says it plans a voluntary licensing program that would allow generic versions before the original patent expires. Exact timelines remain tied to further trials and regulatory review.
“The biggest gap in prevention isn’t medication — it’s accessing medications,” said Dr. Grant.
A path toward ending the HIV epidemic
PURPOSE 1 is part of a broader international effort to end the HIV epidemic by 2030 C.E. — a goal set by the Joint United Nations Programme on HIV/AIDS. Reaching that target will require not just effective tools but affordable, accessible ones.
The shot’s 100% efficacy result is a genuine scientific milestone. Whether it translates into protection for the millions of women who need it most will depend on manufacturing, pricing, and political will — challenges that no clinical trial can solve on its own.
“Cost is going to play into this dramatically,” said Dr. Zucker. “I think and hope we will do everything we can to try to reduce barriers to access.”
Read more
For more on this story, see: NPR
For more from Good News for Humankind, see:
- Alzheimer’s risk cut in half by drug in landmark prevention trial
- U.K. cancer death rates down to their lowest level on record
- The Good News for Humankind archive on global health
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