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The remarkable efficacy of HIV pre-exposure prophylaxis could change the trajectory of the HIV epidemic

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By: Elisavet Serti, PhD

The Joint United Nations Programme on HIV/AIDS (UNAIDS) estimates that in 2013, there were 35 million [33.2–37.2 million] people living with HIV globally, despite widespread awareness of the modes of transmission and the protective benefits of condom use. As of June 2014, only 13.6 million of these people living with HIV had access to antiretroviral therapy. The most alarming statistic is that 19 million of these people do not know their HIV-positive status, according to a new report by UNAIDS. It appears that individuals at risk for HIV infection are still participating in risky sexual behavior and that more education about HIV and AIDS prevention is crucial.

In the United States, complacent attitudes among young adults towards HIV/AIDS infection are on the rise, in part, due to increasingly effective therapies that improve the disease’s manageability. The fact that HIV/AIDS is no longer an automatic “death sentence” could possibly explain lax attitudes among young people when it comes to safe sex practices to avoid infection, such as condom use. As such, the approval of Truveda – a daily, oral pill indicated for pre-exposure prophylaxis (PrEP) – by the Food and Drug Administration (FDA) in 2012 was hailed as a victory by the medical community. Truvada’s safety and efficacy for PrEP were demonstrated in two large, randomized, double-blind, placebo-controlled clinical trials. A PrEP indication means that Truvada is approved for use as part of a comprehensive HIV prevention strategy that includes other prevention methods, such as safe sex practices, risk reduction counseling, and regular HIV testing. In an FDA press release, Truvada was described as “the first drug approved to reduce the risk of HIV infection in uninfected individuals who are at high risk of HIV infection and who may engage in sexual activity with HIV-infected partners. Truvada, taken daily, is to be used for PrEP in combination with safer sex practices to reduce the risk of sexually-acquired HIV infection in adults at high risk.” The FDA Commissioner, Margaret A. Hamburg M.D., marked its approval as “an important milestone in our fight against HIV.”

When HIV researchers showed that people likely to be exposed to HIV could significantly decrease their risk of infection by taking one pill, many researchers immediately raised doubts about the pill’s real-world efficiency. Some scientists and health care workers rejected PrEP stating that this strategy could potentially undermine the traditional and still necessary ways of anti-HIV protection, such as safe-sex practices like condom use. Additionally, some at-risk people have not used PrEP because they fear it will brand them as promiscuous or reckless. Young, single women appear especially reluctant to use the drug, again because of the fear of a social stigma. The pill has also raised controversy in the gay community. The husband of an HIV-positive man who is taking PrEP regularly and remains HIV-negative said in a recent interview, “there’s a real stigma against this drug. Any young gay man that considers using Truvada is viewed as somebody who must be putting himself at great sexual risk for HIV.” It has been shown that men who have sex with men (MSM) carry a disproportionate burden of being infected with HIV compared with general population samples from low- and middle-income countries in the Americas, Asia, and Africa. MSM is a term coined in 1994 to reduce stigma against gay, bisexual, transgendered, and self-identified heterosexual men who engage in sex with other men, by describing behaviors rather than social or cultural identities. The odds for HIV infection in MSM are elevated across prevalence levels of MSM-associated HIV infection by country and decrease as general population prevalence increases, but remain 9-fold higher in medium-high prevalence settings. MSM from low- and middle-income countries are in urgent need of prevention and care, and appear to be both understudied and underserved.

Based on studies conducted primarily outside the United States of both high-risk men who have sex with men and heterosexual couples, Truvada has been shown to reduce the risk of acquiring HIV infection by more than 50% in several subgroups of patients when used daily in combination with a comprehensive HIV prevention strategy, including safer sex practices. The key factor for its effectiveness is the adherence to daily administration. Robert Grant, a top HIV researcher at the Gladstone Institutes and University of California at San Francisco and one of the pioneers of the PrEP approach, led a pivotal study of PrEP in 2010 with remarkable efficiency results. In this study, Truvada cut the rate of new infections in men who have sex with men and transgender women by 92% if they took the pill daily. Unfortunately, half of the participants failed to comply with the daily administration rules, which reduced the overall efficiency to 44%. A follow-up study included a large number of heterosexual “discordant” couples, in which only one partner was infected, found that adherence was much better, yielding 75% protection. There has been a lot scientific controversy from the publication of these studies, with other research groups raising questions about the economic impact of this prevention strategy, the side effects (e.g., renal insufficiency), the potential emergence of drug resistance (in patients with HIV and hepatitis B virus infection), the chance of risk compensation (increased high-risk sexual behavior) of the uninfected recipients of PrEP, and the age difference between experimental groups of the study.

Dr. Grant has continued his PrEP research and published a modeling study of the San Francisco epidemic, in which only 31% of people at high risk of infection used the PrEP regimen at some point last year, showing again that the potential payoff of widespread PrEP could be huge. If 65% of these people used the PrEP regimen for 12 months, the number of annual new infections would be halved. That drop could double again by aggressive use of both PrEP and antiretroviral treatment. “We’re at a tipping point where PrEP was a proven concept of unknown applicability,” Grant stated in a recent Science article, “and what’s most exciting is we can now see that is feasible.”

Dr. Anthony Fauci, who has headed the National Institute of Allergy and Infectious Diseases since 1984 and was one of the leading researchers involved in developing antiretroviral therapy for HIV, stated that Truvada is “highly efficacious, in my mind easily over 90 percent if you adhere rigidly to it.” He was quick to add, in line with the guidelines from all the United States government agencies, that the use of Truvada should be purely a preventive measure, that it’s meant to augment the protection provided by condoms, not to replace them. Still, having one more tool to add to the arsenal against HIV/AIDS is a great step forward in combating the spread of this disease.

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Written by sciencepolicyforall

April 8, 2015 at 9:00 am

Posted in Essays

Tagged with , , ,

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