Weighing the Evidence of Efficacy of Oral PrEP for HIV Prevention in Women in Southern Africa

Abstract

As oral tenofovir-based regimens for preexposure prophylaxis (PrEP) are adopted as standard of care for HIV prevention, their utilization in clinical trials among women in southern Africa will require an accurate estimate of oral PrEP efficacy in this population. This information is critical for women in choosing this prevention strategy, and in public health policy making. Estimates of the efficacy of oral PrEP regimens containing tenofovir have varied widely across trials that enrolled women, with some studies reporting high efficacy and others reporting no efficacy. Although poor adherence is strongly associated with lack of efficacy, other factors, such as mode of transmission (sexual vs. parenteral), predominant HIV subtype (C vs. non-C), intensity of exposure, and percentage of stable serodiscordant couples, may also contribute to the variation in efficacy estimates. In this article, we evaluate the evidence for PrEP efficacy in women and propose potential explanations for the observed differences in efficacy among studies. Our review emphasizes the need to continue to refine estimates of efficacy and effectiveness of tenofovir-based oral PrEP so as to best develop the next generation of HIV prevention tools, and to inform public policies directed toward HIV prevention.

Sexually transmitted infections and HIV in the era of antiretroviral treatment and prevention: the biologic basis for epidemiologic synergy

“…A series of clinical trials demonstrated that TDF/FTC can prevent HIV acquisition in MSM and women [reviewed in ].…”

Incorporating oral PrEP into standard prevention services for South African women: a nested interrupted time-series study

“…Since 2015, trials have navigated a complex path between the evolving process of implementation and access based on in-country PrEP guidelines and decisions about study-specific access to PrEP for trial participants. [10][11][12] Ethical guidance from WHO and UNAIDS has declared that prevention trials should offer an optimised standard of prevention package, incorporating new prevention strategies as they show effectiveness and are incorporated into national policies. 13 The ECHO trial 14 was a randomised trial done to evaluate whether the risk of HIV acquisition differed substantially for women using one of three long-acting reversible contraceptives.…”

Preexposure Prophylaxis for Mitigating Risk of HIV Transmission During HIV Cure–Related Clinical Trials With a Treatment Interruption

“…Nonadherence was identified as the main reason for the failure of these clinical trials. Other factors that have been identified as potential contributors to the lower efficacy of PrEP in women include socioepidemiologic characteristics (eg, transmission route, HIV subtype, exposure intensity, and percentage of population in a stable serodiscordant relationship) and biological features (eg, a difference in the distribution of ART in the female genital tract, compared with sperm or the rectum, and the peculiar composition of the vaginal microbiome) [12]. The Centers for Disease Control and Prevention therefore recommends that PrEP be taken about 20 days before vaginal sex [13].…”