By Medical News Desk
August 1, 2026
The landscape of global HIV prevention has shifted decisively toward long-acting injectable therapy. New data presented at the International AIDS Conference (IAC) in Rio de Janeiro reveal that the twice-yearly injectable lenacapavir (brand name Yeztugo) maintains near-perfect efficacy in preventing HIV infection, according to results from year-long open-label extensions of the landmark PURPOSE 1 and PURPOSE 2 clinical trials.
With only one documented HIV infection across both comprehensive study cohorts during the extension period, researchers are hailing the findings as a "game-changer" for global public health, offering a path toward potentially ending the HIV epidemic through a simplified, highly effective prevention regimen.
The Core Findings: A Near-Total Shield Against HIV
The PURPOSE trials have consistently demonstrated that lenacapavir, administered as a subcutaneous injection every six months, provides robust protection against HIV-1. The open-label extensions, which followed the conclusion of the randomized, blinded phases of the original studies, were designed to assess long-term safety, adherence, and real-world efficacy.
PURPOSE 1: Adolescent Girls and Young Women
In the PURPOSE 1 extension, which focused on adolescent girls and young women in South Africa and Uganda, the results were striking. Among 2,136 participants who continued lenacapavir from the initial trial and 2,496 participants who transitioned from daily oral PrEP (emtricitabine and tenofovir alafenamide or emtricitabine and tenofovir disoproxil fumarate), there were zero new HIV infections recorded during the 52-week extension period.
Dr. Noah Kiwanuka of the Makerere University School of Public Health presented these findings, noting the stark contrast between the randomized phase and the open-label follow-up. "As an investigator at one of the study sites, it has been a deeply meaningful experience to transition from seeing women acquire HIV in the randomized study phase to observing zero new infections in the open-label phase," he stated. The calculated HIV incidence rate for the total lenacapavir person-time in PURPOSE 1 stood at a negligible 0.03 per 100 person-years.
PURPOSE 2: Cisgender Men and Gender-Diverse Populations
The PURPOSE 2 extension, which enrolled cisgender men and transgender or gender-nonbinary individuals, reported similarly compelling results. Among 1,587 participants who continued their lenacapavir regimen, only one new HIV infection was identified. For the 827 participants who switched from daily oral PrEP to the injectable, there were no new infections.
Dr. Marcelo Losso of the Hospital General de Agudos J. M. Ramos Mejía in Buenos Aires, who presented the data, reflected on the significance of these findings. "After 30 years providing care at a public hospital for people living with HIV, it is a profound privilege to be part of an initiative that provides this level of innovation for the populations that need it most," Losso said.
Chronology of a Medical Breakthrough
The success of lenacapavir did not occur in a vacuum. It represents the culmination of years of intensive research into capsid inhibitors, a class of drugs that disrupts the HIV life cycle in multiple stages.
- Initial Clinical Development: Lenacapavir was initially explored for treatment-experienced patients with multi-drug resistant HIV, establishing its safety profile and unique pharmacokinetic properties.
- The PURPOSE Trials Launch: Recognizing the "pill fatigue" associated with daily oral PrEP—a primary barrier to adherence—Gilead Sciences launched the PURPOSE series to test twice-yearly subcutaneous injections.
- The Landmark Efficacy Data: PURPOSE 1 established that twice-yearly lenacapavir reduced HIV incidence by 100% compared to oral standards. PURPOSE 2 confirmed a relative risk reduction of 89% in populations of cisgender men and gender-diverse individuals.
- Regulatory Milestones: Following the positive results of the primary trials, the FDA granted approval for lenacapavir as a PrEP agent, and the CDC subsequently issued strong recommendations for its integration into standard care.
- 2026 Open-Label Extensions: The current data presented in Rio de Janeiro confirm that the efficacy observed in controlled settings remains consistent during the transition to open-label, "real-world" conditions.
Supporting Data: Safety, Adherence, and Tolerability
The widespread adoption of any preventative medication hinges not just on efficacy, but on the willingness of patients to remain on the regimen. The extension data provided clear evidence that lenacapavir is both safe and highly preferred by participants.
Safety Profiles
In both PURPOSE 1 and PURPOSE 2, the rate of serious adverse events (SAEs) remained low and comparable between those who continued treatment and those who switched from oral PrEP.
- PURPOSE 1: Roughly 7% of the continuous-treatment group and 5% of the switch group experienced serious adverse events. Importantly, less than 1% of participants in either group discontinued treatment due to adverse events.
- PURPOSE 2: Similarly, 7% and 3% of the respective groups reported SAEs. Discontinuation due to adverse events was rare, occurring in less than 1% of the continuous-treatment group and 0% of the switch group.
Injection-Site Reactions
One of the primary concerns with injectable therapeutics is the tolerability of the injection site. The data suggests that injection-site reactions (ISRs) were well-managed. Discontinuation of the study due to ISRs occurred in less than 1% of the Purpose 1 cohorts and roughly 1% of the Purpose 2 continuous-treatment group.
Exceptional Adherence
Perhaps the most significant metric for public health success is adherence. When the convenience of a twice-yearly injection is contrasted with the daily burden of oral tablets, the preference is clear. In the switch groups, adherence was remarkably high: 97% of switchers in PURPOSE 1 and 92% in PURPOSE 2 successfully received their third scheduled injection. This high retention rate indicates that once patients switch to an injectable, they are highly likely to remain protected.
Official Responses and Clinical Implications
The medical community has reacted with cautious optimism, balanced by the excitement of having a new tool in the fight against a global epidemic.
The Shift in Strategy
Public health officials are now looking toward the logistical challenges of scaling this intervention. While lenacapavir is highly effective, the challenge lies in global distribution, cost-effectiveness, and training healthcare providers to administer subcutaneous injections in diverse settings, ranging from high-resource urban clinics to rural health outposts in sub-Saharan Africa.
Addressing Health Disparities
The PURPOSE trials were specifically designed to include diverse populations that are often underrepresented in clinical research. By including adolescent girls and young women, as well as transgender and nonbinary individuals, the investigators ensured that the data reflected the populations most vulnerable to HIV transmission.
"The efficacy is undeniable, but the true impact will be measured by how quickly and equitably we can get this into the hands of those who need it," said a spokesperson for the International AIDS Society. "The zero-infection results in the extension phases provide the strongest possible argument for accelerating access programs."
The Path Forward: Implications for the Future
The success of these extensions suggests that the era of daily oral PrEP may be approaching a significant decline, if not an end. However, experts warn against complacency.
- Combination Prevention: Lenacapavir is a potent tool, but it should be viewed as part of a broader strategy that includes testing, treatment for those already living with HIV (U=U), and the management of other sexually transmitted infections.
- Long-Term Monitoring: While the 52-week extension results are stellar, researchers will continue to monitor the long-term impact of biennial injections on viral evolution and potential resistance, although the drug’s unique mechanism of action makes this risk relatively low.
- Global Equity: The ultimate test for lenacapavir will be its deployment in low- and middle-income countries. Gilead Sciences and international health organizations are currently under pressure to ensure that the drug is priced accessibly and that supply chains are robust enough to support biannual dosing schedules for millions of people.
As the delegates leave Rio de Janeiro, the mood is one of renewed determination. The data presented at the IAC does not merely confirm a scientific success story; it offers a tangible, actionable roadmap to a world where HIV infection becomes an increasingly rare event, provided that the global community can muster the political and financial will to deploy these innovations effectively.
With the PURPOSE trial extensions, the scientific community has fulfilled its part of the bargain—delivering a safe, effective, and highly desirable prevention tool. The next chapter will be written by the governments, NGOs, and healthcare systems tasked with bringing this technology to the front lines of the HIV epidemic.
