Twice-Yearly Lenacapavir for HIV Prevention: Phase 3 Trial Results

The Phase 3 PURPOSE 1 and PURPOSE 2 trials found that subcutaneous lenacapavir every 26 weeks was highly effective for HIV prevention. The “100%” result often used in headlines means that no infections were observed in the PURPOSE 1 lenacapavir group during the primary analysis. It does not guarantee 100% protection for every person.

PURPOSE 1 Results

PURPOSE 1 enrolled adolescent girls and young cisgender women in South Africa and Uganda. Among 5,338 participants who did not have HIV at baseline, 55 incident infections occurred overall, but none occurred among the 2,134 participants assigned lenacapavir during the primary analysis. HIV incidence was significantly lower than both the estimated background incidence and the incidence in the F/TDF group.

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PURPOSE 2 Results

PURPOSE 2 included cisgender men, transgender women, transgender men, and nonbinary people who have sex with men. Two HIV infections occurred in the lenacapavir group and nine in the F/TDF group. Incidence with lenacapavir was about 96% lower than estimated background incidence and significantly lower than with F/TDF.

How to Interpret “100%” Correctly

• It is an observed result in the PURPOSE 1 population and study period, not a lifetime individual guarantee.
• Real-world effectiveness depends on confirming HIV-negative status before starting, receiving injections on time, and completing follow-up.
• Lenacapavir does not prevent other STIs or pregnancy.

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Safety and Follow-Up

Injection-site reactions were common, although relatively few participants stopped the trial regimen because of them. HIV testing is required before starting and before each injection, and anyone stopping needs a continuing prevention plan because the medicine remains in the body for a prolonged period. Authorization and availability vary by country, so obtain it only through an authorized healthcare service.

Verified references

Links and relevance to the article’s main topic were reviewed on 13 August 2026. Each source supports only the scope stated in the original document and does not replace personalised medical, legal, or service advice.

1. NEJM: Twice-Yearly Lenacapavir for HIV Prevention in Men and Gender-Diverse Persons Accessed 13 August 2026
2. US FDA: Yeztugo prescribing information Accessed 13 August 2026
3. NIH HIVinfo: HIV Treatment Basics Accessed 13 August 2026