The cost-effectiveness of pre-exposure prophylaxis for HIV infection in South African women

Abstract

Background: Recent trials report the short-term efficacy of tenofovir-based pre-exposure prophylaxis (PrEP) for prevention of human immunodeficiency virus (HIV) infection. PrEP's long-term impact on patient outcomes, population-level transmission, and cost-effectiveness remains unknown.

Methods: We linked data from recent trials to a computer model of HIV acquisition, screening, and care to project lifetime HIV risk, life expectancy (LE), costs, and cost-effectiveness, using 2 PrEP-related strategies among heterosexual South African women: (1) women receiving no PrEP and (2) women not receiving PrEP (a tenofovir-based vaginal microbicide). We used a South African clinical cohort and published data to estimate population demographic characteristics, age-adjusted incidence of HIV infection, and HIV natural history and treatment parameters. Baseline PrEP efficacy (percentage reduction in HIV transmission) was 39% at a monthly cost of $5 per woman. Alternative parameter values were examined in sensitivity analyses.

Results: Among South African women, PrEP reduced mean lifetime HIV risk from 40% to 27% and increased population discounted (undiscounted) LE from 22.51 (41.66) to 23.48 (44.48) years. Lifetime costs of care increased from $7280 to $9890 per woman, resulting in an incremental cost-effectiveness ratio of $2700/year of life saved, and may, under optimistic assumptions, achieve cost savings. Under baseline HIV infection incidence assumptions, PrEP was not cost saving, even assuming an efficacy >60% and a cost <$1. At an HIV infection incidence of 9.1%/year, PrEP achieved cost savings at efficacies ≥50%.

Conclusions: PrEP in South African women is very cost-effective by South African standards, conferring excellent value under virtually all plausible data scenarios. Although optimistic assumptions would be required to achieve cost savings, these represent important benchmarks for future PrEP study design.

Figure 1.

One-way sensitivity analyses: incremental cost-effectiveness of pre-exposure prophylaxis (PrEP). This tornado diagram summarizes the results of multiple 1-way sensitivity analyses on the incremental cost-effectiveness of PrEP. Each horizontal bar represents the range of incremental cost-effectiveness ratios (ICERs) resulting from variations of a given model parameter across its plausible range, as indicated at opposite ends of each bar. The range for each bar is reported in the direction of the ICER for that bar. For example, higher human immunodeficiency virus (HIV) infection incidences and higher PrEP efficacies result in lower PrEP ICERs and are therefore reported from high to low as the bar moves from left to right. The bold vertical line indicates the base case ICER ($2700 per year of life saved). A bar reaching zero on the left would indicate cost saving (none of the bars reach that benchmark). The dashed vertical line represents the per capita gross domestic product (GDP) for South Africa, a threshold denoting a very cost-effective use of resources, by international standards [–20].

Figure 2.

Multiway sensitivity analyses: incremental cost-effectiveness of pre-exposure prophylaxis (PrEP). This figure reports the ranges of incremental cost-effectiveness ratios for PrEP as a function of the 3 most influential parameters identified in Figure 1: human immunodeficiency virus (HIV) infection incidence of 1%–11% annually (vertical axis), PrEP efficacy of 0%–95% (horizontal axis), and PrEP program cost (the 3 vertical panels). The color indicates the incremental cost-effectiveness ratio achieved by each combination of parameters, ranging from not cost-effective in red (ratio >$21 600 per year of life saved [YLS]), to cost-effective in yellow ($7200–21,600/YLS), to very cost-effective in orange (<$7200/YLS), to cost saving in green. A, Base PrEP program costs. B, Base PrEP program costs with 50% reduction in PrEP drug cost (from $55/year to $28/year). C, 50% reduction in base PrEP program costs (from $188/year to $94/year). The base case and CAPRISA 004, iPrEX, TDF2 and Partners PrEP trial point estimates are indicated in each panel by the (+).

Figure 3.

Projected costs per woman over time, without and with pre-exposure prophylaxis (PrEP). This figure presents the components of the cumulative costs at 1, 2, 5, 10, and 20 years and over a woman’s lifetime, with No PrEP and PrEP availability. PrEP costs (shaded blue) are divided by their components, including drug costs only, PrEP monitoring costs (chemistry panels), and human immunodeficiency virus (HIV) testing costs. HIV care costs for those who became infected (shaded orange) include the costs for HIV-related care and antiretroviral therapy (ART; shaded red). Costs are scaled per 1000 people and reported in thousands (2010 US dollars).