[Paper Review] Pre-exposure prophylaxis (PrEP) versus treatment-as-prevention (TasP) for the control of HIV: Where does the balance lie?

Brian Williams, Eleanor Gouws+3 more|arXiv (Cornell University)|Aug 27, 2012

HIV/AIDS Research and Interventions19 references3 citations

TL;DR

This study compares pre-exposure prophylaxis (PrEP) and treatment-as-prevention (TasP) for HIV control, using mathematical modeling to evaluate effectiveness, affordability, and cost-effectiveness. It finds that PrEP is favored over TasP only when HIV incidence exceeds 5% or TasP reduces transmission by more than 50%, recommending PrEP for high-risk groups like young women, MSM, and sex workers in high-burden settings.

ABSTRACT

Anti-retroviral drugs can reduce the infectiousness of people living with HIV by about 96%--treatment as prevention or TasP--and can reduce the risk of being infected by an HIV positive person by about 70%--pre-exposure prophylaxis or PrEP--raising the prospect of using anti-retroviral drugs to stop the epidemic of HIV. The question as to which is more effective, more affordable and more cost effective, and under what conditions, continues to be debated in the scientific literature. Here we compare TasP and PreP in order to determine the conditions under which each strategy is favourable. This analysis suggests that where the incidence of HIV is less than 5% or the risk-reduction under PrEP is less than 50%, TasP is favoured over PrEP; otherwise PrEP is favoured over TasP. The potential for using PreP should therefore be restricted to those among whom the annual incidence of HIV is greater than 5% and TasP reduces transmission by more than 50%. PreP should be considered for commercial sex workers, young women aged about 20 to 25 years, men-who-have-sex with men, or intravenous drug users, but only where the incidence of HIV is high.

Motivation & Objective

• To evaluate the relative effectiveness, affordability, and cost-effectiveness of PrEP versus TasP in controlling HIV transmission.
• To identify the epidemiological conditions under which each strategy is more favorable.
• To guide public health policy on when and for whom to prioritize PrEP or TasP implementation.
• To determine threshold conditions for PrEP deployment based on incidence rates and intervention efficacy.

Proposed method

• The study employs a mathematical modeling framework to simulate HIV transmission dynamics under different intervention scenarios.
• It incorporates two key efficacy parameters: PrEP's risk-reduction (up to 70%) and TasP's transmission-reduction (approximately 96%).
• The model compares outcomes across varying levels of HIV incidence and intervention effectiveness to determine comparative advantages.
• It evaluates cost-effectiveness by analyzing the balance between intervention coverage, incidence reduction, and resource allocation.
• Threshold analysis is used to identify the critical incidence rate (5%) and efficacy level (50%) that determine strategy preference.
• The analysis focuses on specific high-risk populations, including young women, men-who-have-sex-with-men, commercial sex workers, and intravenous drug users.

Experimental results

Research questions

• RQ1 Under what conditions is PrEP more effective than TasP in reducing HIV transmission?
• RQ2 What is the threshold incidence rate at which PrEP becomes more favorable than TasP?
• RQ3 How does the efficacy of TasP influence the relative advantage of PrEP over TasP?
• RQ4 For which high-risk populations is PrEP most likely to be cost-effective and recommended?
• RQ5 What are the implications of combining PrEP and TasP in high-burden settings?

Key findings

• PrEP is favored over TasP when the annual HIV incidence exceeds 5% or when TasP reduces transmission by more than 50%.
• When incidence is below 5% or PrEP's risk-reduction is less than 50%, TasP is more effective and cost-efficient.
• The model identifies a critical threshold of 5% annual HIV incidence as a key decision point for PrEP deployment.
• PrEP should be restricted to populations with high incidence, such as young women aged 20–25, men-who-have-sex-with-men, and intravenous drug users.
• TasP remains the preferred strategy in low-incidence settings due to its higher population-level impact and lower cost per averted infection.
• The findings support targeted PrEP implementation only in high-burden populations where transmission dynamics justify the intervention cost.