Our work focuses on designing optimal HIV prevention strategy to reduce HIV transmission between female-sex workers (FSWs) and their clients. We combine biological, behavioural and cost data from the world largest HIV prevention intervention targetting high-risk groups (including FSWs) the Avahan India AIDS Initiative funded by the Bill & Melinda Gates Foundation (BMGF) and implemented since 2003. Since the impact of Avahan (42% reduction in HIV transmission across all groups) required high cost (around $3 million over 4 years), the aim of our work is to understand how the available resources could have been allocated differently so that similar impact would have been achieved with reduced costs.

Our analysis suggests that the optimal design of HIV prevention programmes for FSWs requires a combination of scalelling up the intervention and increasing intervention intensity. Specifically, as budget levels increase, the optimal intervention strategy is to first increase intervention intensity which achieves little impact, then scale-up coverage to high levels for large increases in impact, and lastly increase intensity further for small additional gains. Cost-effectiveness is poor for low budget levels, improves dramatically as scale is increased, and then reduces once scale is maximised. If intervention intensity and scale had been optimised, Avahan could have achieved the same impact with 10% less budget; but only 13% of the impact could have been achieved with half the budget.

This tailored design of the HIV prevention programmes for FSWs can both improve their impact and cost-effectiveness and this is critical for optimising the use of limited resources for preventing HIV.