AIDS researchers were crestfallen after admitting today that a major clinical trail into anti-HIV gel showed it failed to reduce the risk of infection.

Earlier results had suggested that PRO 2000 – a gel applied to the vagina or rectum to combat virus transmission – could reduce the risk of infection by around 30% but the new trial of 9,385 women found it was no better than placebo.

“This is a disappointing result for the product, as the trial shows that it is not effective,” says Jonathan Weber, co-chair of the Microbicides Development Programme management board and a researcher at Imperial College London (press release). “However, the trial itself was very well designed and undertaken, so we know that the results are definitive.”

Among the 3,156 women given PRO 200 gel there were 130 cases of HIV infection. Among 3,112 given placebo gel there were 123 cases. Trial participants were asked to use the gel both before and after sex and they were also given condoms and asked to use these as well as the gel.

The results will be submitted for peer-review publication, says the Microbicides Development Programme. The MDP notes that although this is “certainly the end of research on PRO 2000, and products with a similar level of potency in the laboratory tests” there are trials of a more potent microbicide called tenofoir already underway.