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The Carraguard microbicide trial, a large study involving more than 6000 South African women, has found that the seaweed-based vaginal gel is safe but does little to protect against HIV.

Researchers around the world had been keenly awaiting the results, announced yesterday , as Carraguard was the most advanced candidate microbicide in development. It was the only product to have completed a phase 3 trial, the last stage of testing required before taking a product to market.

"We are disappointed with the trial results, but we do not see this as a setback for HIV microbicide research," said Khatija Ahmed, the principal investigator at the Carraguard test site in Soshanguve, near Pretoria.

"A lot of knowledge has been gained, and it is a stepping stone for us improve future trials, " she told reporters in a teleconference.

Although condoms are an effective mechanical barrier against HIV, many women report difficulty in getting their male partners to use them. With 39,5-million people infected with HIV worldwide, the hunt is on for new ways to prevent transmission of the virus, including technologies that give women greater control over their own health.

The Carraguard study, funded by the US-based Population Council and the Bill and Melinda Gates Foundation, included 6202 women at three sites in SA, in Cape Town, Durban and Pretoria. The women were divided into two groups, with half getting the Carraguard and the rest getting a dummy version that looked identical. Neither researchers nor volunteers in the two-year trial knew who was getting the product and who a placebo.

All the women were counselled about safe sex, and provided with condoms.

The study found 134 new HIV infections in the Carraguard group, and 151 infections in the placebo group, a result the researchers said was statistically insignificant. This means they could not say whether the difference in the infection rates between the two groups was due to chance or to an effect of the product being tested.

"I have to say I think the results have both good and bad news in them," said Prof Salim Abdool Karim, who directs the Centre for the Aids Programme of Research in SA, and is a microbicide expert.

"The disappointing news is it didn't stop HIV. The good news is that we have the first completed trial of a microbicide, and it shows unequivocally that it is a very safe product.

"This is not a trivial result. We now know we have a safe basis for combination products, and it gives us the opportunity to look for surrogate markers for that safety," he said.

Carraguard is a clear, odourless gel containing carrageenan, a seaweed derivative. It has been used for decades in products such as baby food, skin lotions and toothpaste.