A vaginal gel containing Gilead Sciences’ tenofovir is being hailed as an important scientific breakthrough in the fight against HIV and genital herpes infections for women.

The results of what is being described as a ground-breaking safety and effectiveness study of an antiretroviral microbicide gel have been reported by the Centre for the AIDS Programme of Research in South Africa (CAPRISA) at the International AIDS Conference in Vienna. The gel, containing 1% tenofovir, was found to be 39% effective in reducing a woman's risk of becoming infected with HIV during sex and 51% effective in preventing genital herpes infections.

The CAPRISA 004 trial involved 889 women at high risk of HIV infection at an urban and a rural site in KwaZulu-Natal. Overall, 98 women out of the 889 became HIV positive during the trial, with 38 in the tenofovir gel group and 60 in the placebo gel group. Out of the 434 women who tested negative for herpes at the start of the trial, 29 became infected in the tenofovir group and 58 became infected in the placebo group.

During monthly visits, all participants were provided with HIV risk-reduction counselling, condoms and treatment for sexually transmitted infections, and each was clinically examined for potential side effects and tested for HIV infection. Women in the study were advised to use the gel up to 12 hours before sex and soon after having sex for a maximum of two doses in 24 hours. Participants used the gel for between one and two-and-a-half years and the trial team observed “no substantive safety concerns”.

The CAPRISA researchers also found that the protective effect against HIV and genital herpes increased as use of the tenofovir gel increased. Women who used the gel in more than 80% of their sex acts had a 54% reduction in HIV infections, whereas those who used it in less than half of their sex acts had a 28% reduction.

Tenofovir gel “could fill an important HIV prevention gap by empowering women who are unable to successfully negotiate mutual faithfulness or condom use with their male partners”, said study co- principal investigator, Quarraisha Abdool Karim, associate director of CAPRISA. She added that "this new technology has the potential to alter the course of the HIV epidemic, especially in southern Africa where young women bear the brunt of this devastating disease”.

Taken in pill form, tenofovir, sold by Gilead as Viread, is a common component of various three-drug cocktails used to treat HIV, but in gel form it appears to provide additional protection against herpes, noted co-principal investigator Salim Abdool Karim. He added that the results “are a significant first step toward establishing the effectiveness of antiretroviral drugs for HIV and genital herpes prevention; confirmatory studies are now urgently needed”.