The results, from two studies in Africa, provide unprecedented opportunities to prevent the spread of HIV.
The first study, called the Partners PrEP, involved more than 9000 men and women and took place at nine separate centres in Kenya and Uganda.
Connie Celum at the University of Washington in Seattle and colleagues recruited 4758 couples where one partner of each couple was already infected with HIV. The uninfected partner took a daily tablet of either anti-HIV drug tenofovir, a combination of tenofovir and emtricitabine â€“ another anti-HIV drug â€“ or a placebo.
Just 13 participants taking the combination drug, more commonly known as Truvada, were infected, compared with 78 taking a placebo â€“ a 73 per cent reduction in risk.
Only 18 infections occurred in the group taking tenofovir, a 62 per cent reduction in risk. Taken together, the drug recipients reduced their risk of infection by 68 per cent compared with placebo takers.
“It’s really exciting, just super,” Cate Hankins, chief scientific adviser to UNAIDS.
The results were similar to those from another trial, conducted jointly by the US Centers for Disease Control and the Botswana Ministry of Health. In this study, 1200 HIV-negative, sexually active people from Botswana received either Truvada or a placebo daily. Over two years, only nine people taking Truvada became infected, compared with 24 in the placebo group â€“ a 63 per cent reduction in risk.
Both trials were halted prematurely because the results were so impressive, making it unethical not to offer the treatment to those who had received placebos.
The results from both studies are to be presented next week in Rome, Italy, at the International AIDS Society Conference on HIV Pathogenesis.
Good news for women
In each trial, men and women were equally protected, making these the first studies to show that a daily pill can protect women as successfully as it can men.
A trial last year showed that a vaginal gel containing tenofovir reduced the risk of infection by 39 per cent in women, compared with an inactive gel. But a trial in which Kenyan women received a tenofovir pill daily was halted earlier this year after recipients seemed to be no better protected than those on placebos.
Hankins says that the new studies revive hope that pills can protect women after all.
Drugs for everyone
At this week’s conference, delegates from UNAIDS, the World Health Organization and CDC will also debate possible changes to the WHO’s current guidance on who should be offered antiretroviral drugs.
In recent weeks, researchers have argued for access to the drugs through international aid programmes to be rapidly expanded in countries with the heaviest HIV burdens, and for the focus to be on preventing spread of the virus rather than simply treating those who already have it. One study estimated that expansion of treatment could save 7.4 million lives by 2020.