Is modelling complexity always needed? Insights from modelling PrEP introduction in South Africa

Hannah Grant, Anna M Foss, Charlotte Watts, Graham F Medley, Zindoga Mukandavire

    Research output: Contribution to journalArticlepeer-review

    2 Citations (Scopus)
    29 Downloads (Pure)


    BACKGROUND: Mathematical models can be powerful policymaking tools. Simple, static models are user-friendly for policymakers. More complex, dynamic models account for time-dependent changes but are complicated to understand and produce. Under which conditions are static models adequate? We compare static and dynamic model predictions of whether behavioural disinhibition could undermine the impact of HIV pre-exposure prophylaxis (PrEP) provision to female sex workers in South Africa.

    METHODS: A static model of HIV risk was developed and adapted into a dynamic model. Both models were used to estimate the possible reduction in condom use, following PrEP introduction, without increasing HIV risk. The results were compared over a 20-year time horizon, in two contexts: at epidemic equilibrium and during an increasing epidemic.

    RESULTS: Over time horizons of up to 5 years, the models are consistent. Over longer timeframes, the static model overstates the tolerated reduction in condom use where initial condom use is reasonably high ($\ge$50%) and/or PrEP effectiveness is low ($\le$45%), especially during an increasing epidemic.

    CONCLUSIONS: Static models can provide useful deductions to guide policymaking around the introduction of a new HIV intervention over short-medium time horizons of up to 5 years. Over longer timeframes, static models may not sufficiently emphasise situations of programmatic importance, especially where underlying epidemics are still increasing.

    Original languageEnglish
    Article numberfdz178
    Pages (from-to)e551-e560
    Number of pages10
    JournalJournal of Public Health
    Issue number4
    Early online date6 Feb 2020
    Publication statusPublished - 23 Nov 2020

    Bibliographical note

    This is a pre-copyedited, author-produced version of an article accepted for publication in Journal of Public Health following peer review. The version of record Grant, H, Foss, AM, Watts, C, Medley, GF & Mukandavire, Z 2020, 'Is modelling complexity always needed? Insights from modelling PrEP introduction in South Africa', Journal of Public Health, vol. 42, no. 4, fdz178, pp. e551-e560. is available online at:

    Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders.


    • infectious disease
    • models
    • sexual health

    ASJC Scopus subject areas

    • Public Health, Environmental and Occupational Health


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