Scientists are seeing positive results from the 'treatment as prevention' strategy.

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PARIS: Heterosexuals who take daily AIDS drugs reduce the risk of being infected by the human immunodeficiency virus (HIV) by nearly two-thirds, ground-breaking studies said.

Campaigners hailed what they described as a powerful new weapon in the three-decade war against AIDS.

"This is a major scientific breakthrough which reconfirms the essential role that antiretroviral medicine has to play in the AIDS response," Michel Sidibe, executive director of the U.N. agency UNAIDS said. "These studies could help us to reach the tipping point in the HIV epidemic."

Remarkable results

A trial called Partners PrEP, conducted by the University of Washington, followed 4,758 'sero-discordant' heterosexual couples - in which one person had HIV and the other was uninfected - in Kenya and Uganda.

The uninfected partner received either a dummy pill or a tablet containing either the HIV drug tenofovir or a combination of tenofovir and emtricitabine.

In the group receiving tenofovir, there were 62% fewer infections compared with the placebo group. In the tenofovir/emtricitabine group, there were 73% fewer infections over counterparts taking the placebo.

The results were so remarkable that safety monitors recommended the probe be stopped early, for to continue it would have been unethical.

Lifesaving prevention tools

The second trial, conducted by the U.S. Centres for Disease Control and Prevention (CDC), followed 1,219 uninfected men and women in Botswana who received either placebo or the tenofovir/emtricitabine combination.

Those who received the antiretroviral pill reduced the risk of HIV infection by 63% compared with the placebo group. They are the first trials to show that so-called pre-exposure prophylaxis, or PrEP, can work among heterosexuals.

Last November a study, conducted among sero-discordant homosexual men, found a reduction of 44% in risk among uninfected partners who took HIV drugs. In contrast, a smaller-scale trial, whose preliminary results were published earlier this year, found that PrEP did not protect heterosexual women.

In May, a big study conducted among sero-discordant heterosexual couples in Africa showed early use of drugs by the infected partner slashed the risk of transmitting HIV to the other partner by 96%. Put together, these trials add massively to the argument that the world's AIDS pandemic can be slowed by wider distribution of antiretrovirals, said activists.