Background: HIV incidence remains high in many countries and use of efficacious HIV prevention methods remains limited. HIV prevention cascades have been proposed to assist in the advocacy for and monitoring and improved targeting of HIV prevention programmes, similar to HIV treatment cascades. However, different prevention cascade formulations exist, reflecting their different purposes. This project aimed at developing a unifying HIV prevention cascade framework on which different applications with different requirements could be based.
Description: A series of meetings and seminars was conducted to establish goals of HIV prevention cascades, review prevention cascade models, and develop new models of cascades. Prevention cascade frameworks were applied to existing datasets to understand gaps in data currently collected. A stakeholders meeting and workshop were held in Harare, Zimbabwe, with policy-makers, non-governmental organisations, programme planners, and international and local researchers to consult on the utility and functions of HIV prevention cascades and develop models for prevention cascades.
Lessons learned: Previously proposed HIV prevention cascade models (Lancet HIV issue July 2016) were considered too complex for many intended uses of prevention cascades, especially routine monitoring and advocacy for HIV prevention. Particularly, estimating the impact of HIV prevention (infections averted) (proposed by Garnett et al., 2016) should be seen as a useful but separate modelling exercise.
Instead, a generic HIV prevention cascade model is proposed that consists of three core steps of motivation for using a prevention method, access to this, and effective use of it in a priority population (Figure blue). This cascade is part of a framework that incorporates the explanatory factors underlying gaps in cascade steps and indicates types of interventions to address these (Figure orange/green). The simple core cascade and wider framework reconcile contrasting needs for simple and complex cascade models.
Conclusions/Next steps: The HIV treatment cascade has shown how a framework can become a driving force for treatment programmes and policy. While applications of the proposed HIV prevention cascade framework need piloting and methods for measuring the framework need to be developed and validated, the HIV prevention cascade has similar potential for boosting our HIV prevention efforts to bring about substantial declines in HIV incidence.

A generic and unifying HIV prevention cascade framework. Blue: Core cascade. Orange: Reasons underlying gaps in cascade. Green: Interventions.
[A generic and unifying HIV prevention cascade framework. Blue: Core cascade. Orange: Reasons underlying gaps in cascade. Green: Interventions.]

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