A clinical trial aimed at investigating whether an antiretroviral pill a day could prevent women from getting HIV was abandoned yesterday.
There were high hopes for the trial, as two other similar trials had cut HIV transmission by some 40 percent.
But after the women had been on the pill for a year, there were no differences in HIV infection between women getting it and those getting a placebo, so the trial's review panel recommended that it be abandoned.
"There were no safety or harm concerns. There was simply no progress made," explained investigator Dr Khatija Ahmed from the Setshaba Research Center in Pretoria.
Almost 2 000 HIV negative women, including 1 200 South Africans, were involved in the trial which aimed to see whether Truvada - a combination pill of two ARVs, tenofovir and FTC - could help protect high risk women from HIV.
"The approximate rate of new HIV infections among trial participants was five percent per year," according to Family Health International, which co-ordinated the FEMPrep trial, which also had sites in Kenya and Tanzania.
"A total of 56 new HIV infections had occurred, with an equal number of infections in those participants assigned to Truvada and those assigned to a placebo pill."
The trial was stopped after a routine review of results from the Independent Data Monitoring Committee (IDMC) found that "it will be highly unlikely to be able to demonstrate Truvada's effectiveness in preventing HIV infection in the FEM-PrEP study population even if it continued to its originally planned conclusion".
Ahmed said that there was no problem with the study design, which had been passed by a number of regulatory authorities.
There were high hopes for this trial as two previous trials using tenofovir have shown that the drug can help to reduce HIV infection.
In the one trial (called Caprisa), tenofovir was inserted into the vagina as part of a gel (called a microbicide) and reduced HIV infection by 39 percent in comparison with the placebo gel.
In the other trial (called iPrex), the same combination pill, Truvada, was taken by gay men and cut their HIV risk by 44 percent.
"Obviously, as researchers this is disappointing," said Ahmed. "But it is also enlightening as it raises new questions for us to answer. The microbicide trial used a gel that was inserted vaginally, while in the study involving men who have sex with men, the infection route was rectal. Perhaps there is a difference in the biology of women, which we need to understand.
"There might also have been a problem with adherence. Although the women told us that they had taken Truvada every day, we need to test their drug levels to see whether this really was the case."
Although all the women were counselled to use condoms every time they had sex and were given condoms and oral and injectable contraceptives, there was still a nine percent pregnancy rate in the trial.
This was higher among women who opted to take a daily contraceptive pill than women who opted for an injection, which could mean that these women also did not take the Truvada daily.
Professor Salim Abdool Karim, Pro Vice-Chancellor at the University of KwaZulu-Natal and principal investigator in the microbicide trial, said that "science does not always produce the answer we hope for".
"Thanks to this important trial, we will be able to better understand when, why and how antiretroviral drugs do and do not prevent HIV. I look forward to seeing the complete results and, in particular, an analysis of whether the drug levels in the female genital tract provides any clues to the study's outcome," added Abdool Karim.