The road to prevention methods based on antiretroviral (ARV) drugs is still fraught with challenges, but recent groundbreaking trial results from this promising new field offer greater hope than previous efforts.
In May 2011, the HPTN-052 trial, conducted among couples in which only one partner was HIV-positive, showed that starting people living with HIV on ARVs at a higher CD4 count (which indicates the strength of the immune system) reduced the risk of transmitting HIV to their partners by 96 percent.
In 2010, the iPrEx study showed that a daily dose of the ARV Truvada decreased the risk of HIV-negative men-who-have-sex-with-men (MSM) becoming infected by about 44 percent. However, a similar study among HIV-negative women did not show the same results and was halted in April 2011 due to Truvada's failure to protect the women from infection.
The manufacturers of Truvada, Gilead Sciences Inc, have approached the US Food and Drug Administration for approval to market the medicine as a possible form of HIV prevention.
Findings about the role of ARVs in preventing HIV may be encouraging to countries with a high level of infection, but South African experts at this week's national AIDS conference cautioned that treatment-based prevention still presents a range of questions about how to translate research into practice, deciding which ARV-based prevention to use, who should get it, and whether the country can afford it.
Any ARV-based prevention strategy will likely need to be rolled out to a targeted group, according to Gita Ramjee, director of the HIV Prevention Research Unit at South Africa's health research body, the Medical Research Council,
"To roll out pre-exposure prophylactics (PrEP) is not going to be easy... unless we have a targeted intervention, so we need to identify which is a high [HIV] risk group that will benefit from PrEP," Ramjee told IRIN/PlusNews.
"We can identify high risk in the developed [world], we have men-who-have-sex-with-men and intravenous drug users, but if you look at women in KwaZulu-Natal [South African province], their HIV incidence is as high or even higher than the high-risk group in the developed world, so I think there's going to be a disparity… [in] how we define high risk."
With the exception of microbicides, ARV-based PrEP would have to be taken daily to reduce the risk of HIV infection. Given the use of many first-line HIV medications in ARV-prevention, non-adherence and possible HIV-infection during single-drug PrEP regimens means that large-scale implementation could increase the risk of resistance to first-line drugs.
Resistance is much less likely to occur with the use of microbicides, said Lynne Wilkinson, deputy country director for Médecins Sans Frontières, who cautioned that resistance fears had to be balanced against the benefits of ARV-based prevention.
"I think the resistance issue should not deter implementation of this very important intervention. We clearly need to do something about prevention and, clearly, ARVs are working," she told IRIN/PlusNews.
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"Tenofovir [an ARV] I don't think is the optimal drug to be using," she added. "Right now it's working but I think we need to be moving towards drugs that aren't part of first-line drugs."
Dr Helen Rees, executive director of the Wits Reproductive Health and HIV Institute, said the issue of resistance had also been raised regarding another ARV, nevirapine, which is used for prevention of mother-to-child HIV transmission (PMTCT).
"When we registered single-dose nevirapine, we anguished about what we were going to do for fear of [drug] resistance," Rees said. "The truth is, there is resistance but that doesn't mean the decision to register the drug and the rollout were not absolutely correct."
In the absence of PMTCT intervention, up to 40 percent of babies born to HIV-positive mums will contract HIV before or during birth.
South Africa has now moved to a dual drug PMTCT regimen for improved efficacy, and to reduce resistance.
The near future
At a panel discussion on ARV-based prevention, many agreed that initiating patients on ARVs sooner to prevent new HIV infections was most feasible in the short term. Currently, South Africa initiates most HIV-positive people on drugs when their CD4 count is below 200. To replicate the findings of the HPTN-052 study, HIV patients would have to begin taking ARVs when their CD4 count is at least 350.
Dr Yogan Pillay, deputy director general of Strategic Health Programmes at the Department of Health, said they were evaluating what it would cost to put patients on treatment sooner, but admitted it was hard to project uptake when most South African HIV patients started late, even under existing guidelines.
In a recent report, MSF noted that HIV prevalence among pregnant women in the Cape Town township of Khayelitsha has been declining. More than 85 percent of HIV patients are registering undetectable viral loads - the measure of HIV in their blood - and the organization has partly credited ARV treatment for this.
As a result, and taking into account the outcome of the recent treatment-as-prevention trial, the organization will begin a pilot project later this year in South Africa's high HIV prevalence province of KwaZulu-Natal, in which patients will begin treatment at a CD4 count of 500.