HIV Prevention -- Including PrEP -- a Key Focus of International AIDS Conference

By Liz Highleyman

HIV prevention was a major theme at the XVII International AIDS Conference this month in Mexico City, as it has been at several recent medical meetings. Although the efficacy of and access to antiretroviral therapy continues to improve, experts emphasize that effective prevention is needed to truly curb the epidemic.

Over the past few years, the focus has shifted to biomedical prevention methods -- such as vaccines, microbicides, and pre-exposure prophylaxis (PrEP) -- which many hoped would prove more effective than behavioral change such as increased abstinence or condom use.

But trials of biomedical methods have produced several setbacks, including failure of the STEP vaccine trial, disappointing results from microbicide studies, and data indicating that use of acyclovir to treat genital herpes does not prevent HIV acquisition.

One bright spot in the prevention picture is male circumcision, which has been shown to reduce the risk of HIV infection by 60% or more, a benefit that is sustained for up to 2 years.

Another promising avenue is PrEP, which refers to advance use of antiretroviral drugs prior to HIV exposure. Tenofovir (Viread) is the most widely studied potential PrEP agent; preclinical studies have shown that tenofovir, with or without emtricitabine (Emtriva), reduces the risk of infection in monkeys, but does not eliminate it entirely.

Several clinical trials, including thousands of at-risk individuals, are underway throughout the world. In the meantime, a report by the AIDS Vaccine Advocacy Coalition (AVAC) urges that now is the time to prepare for the results of these studies -- the first of which are expected in 2009 -- which could have a profound impact on future prevention and treatment initiatives.

The drawbacks of long-term use of antiretroviral agents by HIV negative individuals are unclear -- though side effects and increased resistance are among the major concerns -- and the risk-benefit calculation will be different for people who do not need these drugs to control disease progression. Cost effectiveness and limited drug supplies will also be an issue.

"PrEP may prove ineffective. Or it may turn out to be a unique and important new opportunity for the world to reduce HIV infection and change the course of the epidemic," the AVAC report concludes. "People at risk of HIV cannot afford unnecessary delay in PrEP research. Nor can we wait for definitive results before laying plans to utilize PrEP to maximum public health impact against the pandemic."

No one expects that more intensive prevention research will be easy, or that any single method will prove to be a magic bullet. As Nancy Padian and colleagues wrote in an overview in the August 16, 2008 issue of The Lancet, "Biomedical interventions will need to be part of an integrative package that includes biomedical, behavioural, and structural interventions."

UNAIDS Director Peter Piot noted at the AIDS conference that to date advocates have not made the same sort of concerted push for prevention as they have for treatment, but suggested that such activism is now necessary in order to move forward on this front.

8/29/08

Sources

Aids Vaccine Advocacy Coalition. Anticipating the results of PrEP trials. August 2008.

LK Altman. Researchers look to pill, taken daily, to avert HIV. New York Times. August 4, 2008.

B Roehr. Hope for PrEP to prevent HIV. Bay Area Reporter. August 21, 2008.

NS Padian, A Buve, J Balkus, and others. Biomedical interventions to prevent HIV infection: evidence, challenges, and way forward. The Lancet 372(9638): 585-599. August 16, 2008.

J Cohen. Treatment and prevention exchange vows at international conference. Science 321(5891): 902-903. August 15, 2008.