UN and WHO warmly welcome results of study on use of vaginal gel before sexual intercourse

Scientists held out the hope of a breakthrough in the prevention of HIV/Aids today with the results of a study showing that a vaginal gel used by women before sexual intercourse halved the numbers who became infected.

Scientists have been hunting for years for something that will allow women to protect themselves, and the excitement of Aids campaigners will be hard to contain, even though further research is needed to confirm the findings.

Women fall victim to HIV/Aids in disproportionately large numbers – 60% of new infections in Africa are among women. Many in the poorest countries have little education and suffer from very low status, so are unable to negotiate safe sex, using a condom, with their partner.

"We are giving hope to women," said Michel Sidibé, executive director of Unaids, the United Nations programme on Aids, as the trial results emerged. "For the first time we have seen results for a woman-initiated and controlled HIV prevention option. If confirmed, a microbicide will be a powerful option for the prevention revolution and help us break the trajectory of the Aids epidemic."

The director general of the World Health Organisation (WHO), Margaret Chan, also immediately congratulated the scientists. If their results were confirmed by further tests, "WHO will work with countries and partners to accelerate access to these products," she said.

A number of large microbicide trials have been run, but all have failed. The success of this one (run in South Africa where one in three young women aged 20 to 34 is living with HIV) is attributed to the use of an anti-retroviral drug called tenofovir – of the sort used to treat Aids – in gel form.

The study, called Caprisa 004, was conducted by the Centre for the Aids Programme of Research at the University of KwaZulu Natal in South Africa. The researchers recruited 889 women between 18 and 40 who were HIV-negative, sexually active and at risk of becoming infected.

Half were given vaginal applicators filled with gel containing 1% tenofovir. The others got something that looked the same but was inactive. Until the end of the trial, nobody knew who was in each group. The women were asked to insert a first dose of gel 12 hours before sexual intercourse and a second dose as soon as possible afterwards, within 12 hours. All were given counselling on avoiding HIV infection and a free supply of condoms.

At the end of a year, the researchers discovered that the gel had halved the numbers of women becoming infected with HIV. After two and a half years, the numbers had dropped, but there were still 39% fewer infections in those women using it. The drop in the numbers protected, they believe, is caused by some women tending to use it inconsistently as time went on, not knowing whether it was in fact having any effect.

The excitement of the researchers was clear in a teleconference before publication. "Picture a young woman in a rural community in South Africa who walks through my clinic doors asking me what I have to protect her from getting infected," said Dr Quarraisha Abdool Karim, one of the authors of the paper. "Her partner is a migrant worker and refuses to wear a condom and she is not sure of his faithfulness in this relationship.

"From being able to tell her for years that I have nothing, I can now offer her 1% tenofovir gel, which offers her 39% protection and, if she is highly attuned to this gel [uses it consistently], it offers her 54% protection."

Warren Mitchell, executive director of Avac, an Aids vaccine campaigning group, said it was "a historic day for HIV prevention research". The results demanded immediate action in South Africa and around the world, he said. "We believe that the most responsible plan of action now is to quickly and efficiently articulate the sequence of steps necessary for confirmation and follow-up of these results, while also aggressively planning for potential roll-out of a licensable product."

Another piece of good news is that the gel appeared to cause few side-effects. There is still work to do before the gel goes through to being manufactured.

But the WHO is committed to help and all agencies will do their best to speed it to women who need it, perhaps within two years, the researchers said.

• The headline on this article was amended on 20 July 2010. The original referred to the risk of infection by Aids. This has been corrected to infection by HIV.