The first anti-AIDS vaginal gel to make it through late-stage testing failed to stop HIV infection in a study of 6,000 South African women, disappointed researchers announced Monday.

The study was marred by low use of the gel, which could have undermined results, they said. Women used it less than half the number of times they had sex, and only 10 percent said they used it every time as directed.

Scientists are still analyzing the results to see if this made a difference. They also plan more tests on a revamped gel containing an AIDS drug that they hope will work better.

The gel used in the current study did prove safe, however, and researchers called that a watershed event.

But for now, the effort is the latest disappointment in two decades of trying to develop a microbicide – a cream or gel women could use to lower their risk of getting HIV through sex. A female-controlled method is especially needed in poor countries where women often can’t persuade men to use condoms.