A new study has added to growing evidence that a daily dose of antiretroviral treatment taken by the HIV-negative partner in a heterosexual, HIV-discordant relationship can significantly reduce the risk of HIV transmission.
The Partners PrEP trial, the largest to date to consider the effectiveness of pre-exposure prophylaxis (PrEP) for HIV prevention, involved 4,758 HIV-negative people in Kenya and Uganda, all with HIV-positive partners. One-third of HIV-negative participants took a daily tablet of the antiretroviral, tenofovir; one-third a combination of tenofovir and emtricitabine; and the rest a placebo. The trial, begun in July 2008 and conducted by the University of Washington's International Clinical Research Centre, ended a year early due to the overwhelming evidence produced.
Risk redused by 62%
"We found that the people [taking] tenofovir... had an average of 62% fewer HIV infections than those [taking] the placebo... while participants [on] the combination... had 73% fewer infections than those [on] the placebo," Jared Baeten, lead investigator of the trial and assistant professor of global health and medicine at the University of Washington, told IRIN/PlusNews.
Participants in all parts of the study were offered a comprehensive HIV prevention package before and during the trial. Adherence to the daily PrEP medication was very high, with more than 97% of dispensed doses taken.
A second study conducted by the US Centres for Disease Control released similar results on 13 July. Named TDF2, it involved 1,200 heterosexual men and women in Botswana and found that 62.6% fewer HIV infections had occurred in participants taking a combination of tenofovir and emtricitabine compared with the placebo group.
"These results show that it is time for national governments to evaluate and incorporate PrEP into HIV policy," said Baeten.
The study will be completed as investigators continue to monitor participants' tolerance of the drugs; the participants on the placebo will be placed on ARVs.
In May, a major randomised clinical trial found that treating an HIV-infected individual can reduce the risk of sexual transmission of HIV to an uninfected partner by as much as 96%. In 2010, the Centre for the AIDS Programme of Research in South Africa (CAPRISA) found that a vaginal gel containing tenofovir was 39% effective in reducing a woman's HIV risk when used for about three-quarters of sex acts and 54% effective when used more consistently. Also in 2010, the Iniciativa Profilaxis Preexposicion or Prexposure Prophylaxis Initiative (iPrEx) study found that daily oral PrEP reduced HIV infection risk among men who have sex with men and transgender people who took a combination of tenofovir and emtricitabine by an average of 43.8%.
"Our study reaffirms the importance of the argument for treatment as prevention; we are not pitting prevention against treatment - the two can work together to change the epidemic in a way that they couldn't individually," Baeten added.
Handle with care
Nelly Mugo, one of the study's Kenyan investigators, said moving PrEP from research to policy needed to be handled carefully.
"The challenge is to find the people most at risk; it's not like iodine in salt - ARVs are not for everyone," she told IRIN/PlusNews. "NASCOP [Kenya's National AIDS and Sexually transmitted infections Control Programme] needs to think keenly about how to find and target people at risk without creating stigma."
Mugo further emphasised that for treatment as prevention and PrEP to work, it would be imperative for more people to be tested for HIV. "Currently, [fewer] than 60% of Kenyans know their HIV status; those numbers have to go up in order to know who is HIV-positive and needs to start on ARVs earlier and who is HIV-negative but at high risk and needs to start taking PrEP," she said.
"Overall, the findings are very exciting and PrEP is a wonderful package, but it needs to be rolled out with care."
Research continues into the effectiveness of PrEP, with investigators in the 5,000-women, five-arm Vaginal and Oral Interventions to Control the Epidemic (VOICE) trial saying it would continue as designed as they evaluate the Partners PrEP and TDF2 trial results. The investigators note that while the results are encouraging, they raise more questions about what happened with FEM-PrEP, a three-country study that was halted in April 2011 after daily doses of a combination of tenofovir and emtricitabine failed to prevent HIV infection in participating women.
UNAIDS and the UN World Health Organisation have hailed the results of the Partners PrEP and the TDF2 study, with Michel Sidibé, executive director of UNAIDS, saying the studies could "help us to reach the tipping point in the HIV epidemic".
UNAIDS and the World Health Organisation have already been working with countries in sub-Saharan Africa, Latin America and Asia to explore the potential role of PrEP in HIV prevention.
"In Kenya and Tanzania we have held regional stakeholders' meetings to discuss the potential role of PrEP should the results of these trials be positive," Kate Hankins, chief scientific adviser to UNAIDS, told IRIN/PlusNews. "In Kenya in particular, we will now be looking at where and how we can use PrEP; whether to integrate it with male circumcision, or to use it in PMTCT with HIV-negative male partners of pregnant women... it will take some thinking." - (PlusNews, July 2011)
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