In a major breakthrough that opens up a new method to protect people HIV infection that causes AIDS, an antiretroviral drug used in the form of a vaginal gel halved HIV infection in women who used it for one year.
The gel also offered 51 per cent protection against sexually transmitted infection called herpes simplex virus-2 - a lifelong incurable infection that puts those infected at a two-to-three times higher risk of acquiring HIV.
The path breaking findings were announced by the International Partnerships for Microbicides at the 18th International AIDS Conference in Vienna on Tuesday.
Globally, more than 33 million people are infected with HIV and AIDS, which has killed 25 million since it was first identified in 1981.
India has 2.27 million people infected with HIV, the last year for which data is available. Of these, 39 per cent were women and 3.5 per cent children.
The gel has the potential to save millions of lives by reducing transmission through unprotected sex, which accounts for almost 89 per cent of HIV transmission in India.
An estimated 1.8 million people are in the high-risk category that includes sex workers, homosexuals, migrants and injected drug users, shows data from the National AIDS Control Organisation.
"These results are a milestone for HIV prevention. For the first time, it's been proved that antiretroviral drugs (used to treat AIDS) applied to the vaginal mucosa can offer protection against HIV and other sexually-transmitted infections," said Dr Zeda Rosenberg, CEO, International Partnerships for Microbicides.
The landmark trial, called CAPRISA 004 (Centre for the AIDS Programme of Research in South Africa), involved 889 rural and urban South African women between 18 and 40 years.
The gel contained 1 per cent tenofovir, an approved drug that interferes with the replication of HIV and is prescribed in tablet form in combination with other AIDS drugs.
The protection, however, fell from 50 per cent in the first year to 39 per cent after 30 months of use. Researchers said the lower level of effectiveness in the second year was because women who got infected over one year used it less regularly or not at all. Adherence to gel use before and after sex increased protection.
It offered 54 per cent protection to women who used two doses 80 per cent of the time they had sex, 38 per cent among women who used it in less than 80 per cent encounters, and 28 per cent among those who used it in fewer than 50 per cent times.