The UNAIDS Modes of Transmission (MoT) model has been used by 29 countries to analyse their HIV epidemics, with the results helping to guide and focus interventions. However, there is the risk that the simplifications inherent in the MoT produce misleading findings. Using input data from Nigeria, this paper compares projections from the MoT with those from a revised model that incorporates additional heterogeneity.
Researchers revised the MoT to explicitly incorporate brothel and street-based sex work, transactional sex (TS), and HIV-discordant couples. Both models were parameterised using behavioural and epidemiological data from Cross River State, Nigeria. Model projections were compared, and the robustness of the revised model projections to different model assumptions, was investigated.
- The original MoT predicts 21% of new infections occur in most-at-risk populations (MARPs), compared with 45% (40 - 75%, 95%) once additional heterogeneity and updated parameterisation is incorporated.
- Discordant couples, a subgroup previously not explicitly modelled, are predicted to contribute a third of new HIV infections.
- Women engaging in TS may be an important but previously less recognised risk group, with 16% of infections occurring in this subgroup.
This study shows that the UNAIDS MoT remains an accessible and potentially useful model that can help inform intervention priorities. However, it argues that the current model may produce misleading findings, especially in more concentrated HIV epidemic settings. Results from this study indicate the need for a formal review of the MoT, and for further revisions to be made.