Informing the development of transmission modelling guidance for global immunization decision-making: A qualitative needs assessment.

In recent years, mathematical transmission models have been increasingly used to support immunization program decisions and to measure the impact and cost-effectiveness of interventions. However, countries face expertise-and resource-related barriers that limit the use and application of modelled evidence to inform decisions. The World Health Organization (WHO) established an Immunization and Vaccines Implementation Research advisory committee subgroup in 2023 to support immunization decision-makers to effectively generate, translate and use such evidence for strategies, policies, and programs. This study supports this effort, detailing the needs of end-users to inform content and format of the guidance. Fifteen in-depth interviews were conducted with vaccination decision-makers and modelers from all six WHO regions and across low-, middle- and high-income countries. Interviews explored: (i) how modelling is understood and used; (ii) the challenges faced when using modelled evidence; (iii) the types of guidance that would be most useful to enhance the use of modelled evidence. Analysis of transcripts was guided by the framework method, which structures the analysis of qualitative data. Participants with modelling expertise used it firsthand, systematically, and often in an advisory capacity. Less experienced users, often in policy advisory roles, were less confident in their understanding of modelling and some did not use it at all. Decision-makers with little or no modelling experience cited a need for more information to help them understand the value of modelling in their context and many supported its potential. All participants saw a need for capacity strengthening and localised application to instil confidence in using modelled evidence. Those with less experience expressed a need for ongoing interactive engagement with knowledge brokers and training. Insights from this study are being integrated into the development of guidance by WHO. By considering the diverse challenges and needs of both experienced and inexperienced users of modelling, the guidance will support immunization strategy and policy by responding specifically to immunization decision-makers information needs.