The Potential Impact of Pre-Exposure Prophylaxis for HIV Prevention among Men Who Have Sex with Men and Transwomen in Lima, Peru: A Mathematical Modelling Study

Abstract

HIV pre-exposure prophylaxis (PrEP), the use of antiretroviral drugs by uninfected individuals to prevent HIV infection, has demonstrated effectiveness in preventing acquisition in a high-risk population of men who have sex with men (MSM). Consequently, there is a need to understand if and how PrEP can be used cost-effectively to prevent HIV infection in such populations. We developed a mathematical model representing the HIV epidemic among MSM and transwomen (male-to-female transgender individuals) in Lima, Peru, as a test case. PrEP effectiveness in the model is assumed to result from the combination of a “conditional efficacy” parameter and an adherence parameter. Annual operating costs from a health provider perspective were based on the US Centers for Disease Control and Prevention interim guidelines for PrEP use. The model was used to investigate the population-level impact, cost, and cost-effectiveness of PrEP under a range of implementation scenarios. The epidemiological impact of PrEP is largely driven by programme characteristics. For a modest PrEP coverage of 5%, over 8% of infections could be averted in a programme prioritising those at higher risk and attaining the adherence levels of the Pre-Exposure Prophylaxis Initiative study. Across all scenarios, the highest estimated cost per disability-adjusted life year averted (uniform strategy for a coverage level of 20%, US$1,036–US$4,254) is below the World Health Organization recommended threshold for cost-effective interventions, while only certain optimistic scenarios (low coverage of 5% and some or high prioritisation) are likely to be cost-effective using the World Bank threshold. The impact of PrEP is reduced if those on PrEP decrease condom use, but only extreme behaviour changes among non-adherers (over 80% reduction in condom use) and a low PrEP conditional efficacy (40%) would adversely impact the epidemic. However, PrEP will not arrest HIV transmission in isolation because of its incomplete effectiveness and dependence on adherence, and because the high cost of programmes limits the coverage levels that could potentially be attained. A strategic PrEP intervention could be a cost-effective addition to existing HIV prevention strategies for MSM populations. However, despite being cost-effective, a substantial expenditure would be required to generate significant reductions in incidence. Please see later in the article for the Editors' Summary Without a vaccine, the only ways to halt the global HIV epidemic are prevention strategies that reduce transmission of the HIV virus. Up until recently, behavioral strategies such as condom use and reduction of sexual partners have been at the center of HIV prevention. In the past few years, several biological prevention measures have also been shown to be effective in reducing (though not completely preventing) HIV transmission. These include male circumcision, treatment for prevention (giving antiretroviral drugs to HIV-infected people, before they need it for their own health, to reduce their infectiousness) and pre-exposure prophylaxis (or PrEP), in which HIV-negative people use antiretroviral drugs to protect themselves from infection. One PrEP regimen (a daily pill containing two different antiretrovirals) has been shown in a clinical trial to reduce new infections by 44% in of men who have sex with men (MSM). In July 2012, the US Food and Drug Administration approved this PrEP regimen to reduce the risk of HIV infection in uninfected men and women who are at high risk of HIV infection and who may engage in sexual activity with HIV-infected partners. The approval makes it clear that PrEP needs to be used in combination with safe sex practices. Clinical trials have shown that PrEP can reduce HIV infections among participants, but they have not examined the consequences PrEP could have at the population level. Before decision-makers can decide whether to invest in PrEP programs, they need to know about the costs and benefits at the population level. Besides the price of the drug itself, the costs include HIV testing before starting PrEP, as well as regular tests thereafter. The health benefits of reducing new HIV infections are calculated in “disability-adjusted life years” (or DALYs) averted. One DALY is equal to one year of healthy life lost. Other benefits include future savings in lifelong HIV/AIDS treatment for every person whose infection is prevented by PrEP. This study estimates the potential costs and health benefits of several hypothetical PrEP roll-out scenarios among the community of MSM in Lima, Peru. The scientists chose this community because many of the participants in the clinical trial that showed that PrEP can reduce infections came from this community, and they therefore have some knowledge on how PrEP affects HIV infection rates and behavior in this population. Because the HIV epidemic in Lima is concentrated among MSM, similar to most of Latin America and several other developed countries, the results might also be relevant for the evaluation of PrEP in other places. For their scenarios, the researchers looked at “high coverage” and “low coverage” scenarios, in which 20% and 5% of uninfected individuals use PrEP, respectively. They also divided the MSM community into those at lower risk of becoming infected and those at higher risk. The latter group consisted of transwomen at higher risk (transsexuals and transvestites with many sexual partners) and male sex workers. In a “uniform coverage” scenario, PrEP is equally distributed among all MSM. “Prioritized scenarios” cover transwomen at higher risk and sex workers preferentially. Two additional important factors for the estimated benefits are treatment adherence (i.e., whether people take the pills they have been prescribed faithfully over long periods of time even though they are not sick) and changes in risk behavior (i.e., whether the perceived protection provided by PrEP leads to more unprotected sex). The cost estimates for PrEP included the costs of the drug itself and HIV tests prior to PrEP prescription and at three-month intervals thereafter, as well as outreach and counseling services and condom and lubricant promotion and provision. To judge whether under the various scenarios PrEP is cost-effective, the researchers applied two commonly used but different cost-effectiveness thresholds. The World Health Organization's WHO-CHOICE initiative considers an intervention cost-effective if its cost is less than three times the gross domestic product (GDP) per capita per DALY averted. For Peru, this means an intervention should cost less than US$16,302 per DALY. The World Bank has more stringent criteria: it considers an intervention cost-effective for a middle-income country like Peru if it costs less than US$500 per DALY averted. The researchers estimate that PrEP is cost-effective in Lima's MSM population for most scenarios by WHO-CHOICE guidelines. Only scenarios that prioritize PrEP to those most likely to become infected (i.e., transwomen at higher risk and sex workers) are cost-effective (and only barely) by the more stringent World Bank criteria. If the savings on antiretroviral drugs to treat people with HIV (those who would have become infected without PrEP) are included in the calculation, most scenarios become cost-effective, even under World Bank criteria. The most cost-effective scenario, namely, having a modest coverage of 5%, prioritizing PrEP to transwomen at higher risk and sex workers, and assuming fairly high adherence levels among PrEP recipients, is estimated to avert about 8% of new infections among this community over ten years. These findings suggest that under some circumstances, PrEP could be a cost-effective tool to reduce new HIV infections. However, as the researchers discuss, PrEP is expensive and only partly effective. Moreover, its effectiveness depends on two behavioral factors—adherence to a strict drug regimen and continued practicing of safe sex—both of which remain hard to predict. As a consequence, PrEP alone is not a valid strategy to prevent new HIV infections. It needs instead to be considered as one of several available tools. If and when PrEP is chosen as part of an integrated prevention strategy will depend on the specific target population, the overall funds available, and how well its cost-effectiveness compares with other prevention measures. Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001323.