Identifying priority populations for HIV interventions using acquisition and transmission indicators: a combined analysis of 15 mathematical models from ten African countries

Abstract

Background: Characterising disparities in HIV infection across populations by gender, age, and HIV risk is key information to guide intervention priorities. We aimed to assess how indicators measuring HIV acquisitions, transmissions, or potential long-term infections influence estimates of the contribution of different populations to new infections, including key populations (including female sex workers, their clients, men who have sex with men).

Methods: In this mathematical model comparison analysis, we evaluated four indicators using nine models representing 15 different settings across Africa. The acquisition indicator (I₁) measured the annual proportion of all new infections acquired by a specific population, the direct transmission indicator (I₂) measured the annual proportion of all new infections directly transmitted by a specific population, and the 1-year transmission population-attributable fractions (tPAFs; I₃) and 10-year tPAFs (I₄) measured the proportion of new infections averted if transmission involving a specific population was blocked over a specific time period. We compared estimates of the four indicators across seven populations and 15 settings and assessed if the contribution of specific populations ranked differently across indicators for ten settings.

Findings: Different indicators identified distinct priority populations as the largest contributors: I₁ identified women aged 25 years and older outside key populations as contributing the most to acquired infections in eight of ten settings in 2020, but to direct transmissions (I₂) in only two settings. In six of ten settings, I₄ identified non-key population men aged 25 years and older and clients of female sex workers as the largest contributors to HIV transmission. Notably, non-key population women aged 15-24 years acquired (I₁) more infections in 2020 (median of 1·7 times higher across models) than they directly transmitted (I₂), whereas more infections were transmitted than acquired in non-key population men aged 25 years and older (median 1·4 times more) and clients of female sex workers (1·6 times more) in all but one model. Estimates of the 10-year tPAFs accounting for transmission in the long-term were substantially larger than the direct transmission indicator for all populations, especially for female sex workers (2·0 times higher).

Interpretation: Indicators that reflect HIV acquisitions and transmissions in the short and long term can be used to capture the complexity of HIV epidemics across different populations and timeframes. The added nuance would improve the effectiveness of the HIV prevention response across all populations at risk.

Funding: US National Institutes of Health and UK Medical Research Council.

Translation: For the French translation of the abstract see Supplementary Materials section.