Scale-up influences and definitions of scale-up 'success': evidence from globally scaled interventions

The World Health Organization ExpandNet framework for scaling up contains key recommendations to support the scaling of health interventions globally. Despite being widely used, it is not known how the framework informs intervention scale-up nor how 'successful' scale-up is defined. Using data from the Scaling Up InTErventions' study, this paper assessed adoption of framework components using an international sample of scaled-up physical activity and nutrition interventions, and explored individuals' definitions of scale-up 'success'. An online survey with academic, community, and government representatives involved in scaling physical activity and nutrition interventions globally. Survey questions (n = 27) corresponded to 32 components of the ExpandNet framework, reflecting four core areas: (i) intervention; (ii) user organization; (iii) resource team; and (iv) scale-up strategy. Data were analysed descriptively and qualitative free-text survey responses coded thematically. In total, 62 survey responses were obtained [academia (n = 32), community (n = 20), and government (n = 10)], corresponding to 35 scaled-up interventions. Only 8% of participants reported all 32 framework components during scale-up. Four core elements (containing eight themes) underpinned successful scale-up: (i) scaling inputs (e.g., sustained partner buy-in); (ii) scaling outputs (e.g., sustained, quality implementation); (iii) scaling outcomes (e.g., increased and equitable reach, improved organization and system capacity) and; (iv) scaling context (e.g., partner mental models, and a context-specific construct). There is no universal definition of successful scale-up. We propose core elements of 'successful scale-up' that could be used as criteria for scale-up planning and evaluation, and are applicable to other areas of public health.