How can we improve the UNAIDS modes of transmission model?

The HIV modes of transmission model: a systematic review of its findings and adherence to guidelines.

Shubber Z, Mishra S, Vesga JF, Boily MC. J Int AIDS Soc. 2014 Jun 23;17:18928. doi: 10.7448/IAS.17.1.18928. eCollection 2014.

Introduction: The HIV Modes of Transmission (MOT) model estimates the annual fraction of new HIV infections (FNI) acquired by different risk groups. It was designed to guide country-specific HIV prevention policies. To determine if the MOT produced context-specific recommendations, we analyzed MOT Results by region and epidemic type, and explored the factors (e.g. data used to estimate parameter inputs, adherence to guidelines) influencing the differences.

Methods: We systematically searched MEDLINE, EMBASE and UNAIDS reports, and contacted UNAIDS country directors for published MOT Results from MOT inception (2003) to 25 September 2012.

Results: We retrieved four journal articles and 20 UNAIDS reports covering 29 countries. In 13 countries, the largest FNI (range 26 to 63%) was acquired by the low-risk group and increased with low-risk population size. The FNI among female sex workers (FSWs) remained low (median 1.3%, range 0.04 to 14.4%), with little variability by region and epidemic type despite variability in sexual behaviour. In India and Thailand, where FSWs play an important role in transmission, the FNI among FSWs was 2 and 4%, respectively. In contrast, the FNI among men who have sex with men (MSM) varied across regions (range 0.1 to 89%) and increased with MSM population size. The FNI among people who inject drugs (PWID, range 0 to 82%) was largest in early-phase epidemics with low overall HIV prevalence. Most MOT studies were conducted and reported as per guidelines but data quality remains an issue.

Conclusions: Although countries are generally performing the MOT as per guidelines, there is little variation in the FNI (except among MSM and PWID) by region and epidemic type. Homogeneity in MOT FNI for FSWs, clients and low-risk groups may limit the utility of MOT for guiding country-specific interventions in heterosexual HIV epidemics.

 Abstract  Full-text [free] access

Editor’s notes: In 2002, the HIV Modes of Transmission model (MoT) was developed by UNAIDS to inform and focus, country-specific HIV prevention policies. The idea behind the model was to use simple mathematical modelling approaches, in combination with country specific data, to predict what the distribution of new HIV infection may look like. In this way, countries would be able to better focus their HIV response. Since its development and through 2012, the MoT has been applied in 29 countries, with the findings being used in many settings to shape priorities. In this study, the authors assess the degree to which the MoT produces different outputs in different epidemic contexts. They explore whether there are key parameters in the model that seem to drive similarities and/or differences in projections between countries. Surprisingly, across a broad range of epidemic settings, they found limited variability in the predicted annual fraction of new HIV infections (FNI) acquired by female sex workers (FSW) (0.04-14.4%). There were higher levels of variability between countries in the projected fraction of new HIV infections among men who have sex with men (0.01-89%) and people who inject drugs (0-82%).

The differences in the MoT projections were largely dependent on whether the country in question was categorised as having a concentrated / low-level epidemic, versus generalised epidemic, as defined by UNAIDS. Differences also arose depending upon whether ‘low risk groups’ were also included in the model. Indeed, for 22 of the 25 studies that included a low-risk group, this group was predicted to have a large annual fraction of new HIV infections (11.8-62.9%). This phenomenon arose, not because of high transmission rates in this group (in comparison to others such as MSM or PWIDs) but because these ‘low risk groups’ are large. They are one third of the total population. These findings may be misleading, as the projected high fraction of transmission is dependent on the assumption that everyone in this ‘low risk group’ does have some risk.

It appears that although the MoT was designed to address an important need, it is likely to have limited utility to guide programming in heterosexually driven epidemics.  To address this limitation, UNAIDS is supporting the HIV Modelling Consortium in their development of a revised MoT model that takes into better consideration risk categorization, data constraints and programmatic needs. The revised model is currently undergoing field testing and will be available for country use in 2015.

Africa, Asia, Europe, Latin America
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