The efficacy and cost-effectiveness of the E-Dengue early warning system-informed proactive interventions to reduce dengue incidence in the Mekong Delta Region of Vietnam.

+ INTERVENTION TOOL: The model-based digital prediction tool for dengue (E-Dengue) The ensemble prediction model combines six complementary statistical models to predict dengue incidence and outbreaks one, two, and three months in advance at the level of the Regional Health Center (RHC). Each model captures different aspects of dengue transmission from seasonal patterns to climate influences on the spatial spread of the disease, providing probabilistic forecasts. Model inputs include climatic data (e.g., temperature, precipitation) and monthly dengue incidence. + INTERVENTION PROCEDURE: Proactive intervention measures and study procedures: Although E-Dengue predicts outbreaks one, two, and three months in advance, the proactive intervention will only be triggered for outbreaks forecast 3 months in advance, as there would not be enough time to mobilize a proactive intervention with a 1- or 2-month lead time. Alerts will be generated monthly during the dengue transmission season (April to November). The first alerts will be issued in late February 2026 (around the 20th of February), once January surveillance data are available, to provide forecasts utilizing data through January 2026 to predict outbreaks occurring in April. Subsequently, alerts will be issued around the 20th of each month (i.e., March-September), as soon as the surveillance data are available for the previous month. The proactive intervention will be physical breeding source reduction combined with health education, information, and communication (EIC). Given the need for sustainable breeding reduction, an RHC will receive the proactive intervention for every month for which it receives an alert, including alerts received in consecutive months (i.e., all alerts will trigger the proactive intervention, and no months will be skipped). Outbreak alerts will be generated monthly from E-Dengue and communicated through the study team at the National Institute of Hygiene and Epidemiology (NIHE) to staff of the provincial Centres for Disease Control (CDC), who subsequently inform commune health staff. These alerts will be used to trigger the proactive intervention and larvae investigation in the intervention RHCs, but only larvae investigation in non-intervention RHCs. In intervention RHCs, due to resource limitations, the proactive source reduction measures will be implemented by provincial and commune health staff in communes with the historically highest number of dengue cases, accounting for at least 50 per cent of cases within each alerted RHC, identified a priori. The source reduction will be delivered within 2 weeks of the forecasting alert, after planning, community mobilisation, and resource allocation have been completed. The EIC intervention will consist of approximately 5-minute health education messages delivered through the commune's stationary loudspeaker systems across all communes within the RHC boundaries. Messages will be broadcast repeatedly for 4 hours per day on 3 days during the week when source reduction activities are triggered, followed by continued broadcasting for the subsequent 3 weeks at a frequency of 1 day per week. In addition, portable loudspeakers will be used at public gathering places such as schools, markets, and religious venues during the EIC period. The EIC messages will include information about dengue risk in the area, guidance about larvae elimination measures, and legal regulations about larva-infected water containers and their elimination. Implementation of the EIC intervention will be planned by provincial CDC staff and implemented by the commune health station (CHS) staff. EIC activities will be reported by the CHS staff following the National forms and monitored by the study team. Physical source reduction will be implemented for the whole commune by dengue community teams consisting of at least 3 to 4 persons per team. Each team will visit 60 to 70 households per source reduction and will conduct intervention measures to treat at-risk water containers and vector breeding habitats by, for example, disposing of discarded items that can hold standing water (e.g., tires, plastic bags, discarded tins, unused water containers), scrubbing the containers or releasing lavivorous fish into them, and covering water containers with lids and screens. If actual dengue outbreaks (as opposed to outbreaks predicted 3 months in advance) are identified in intervention RHCs, the standard routine response measures will be implemented, including source reduction combined with adulticide application and EIC, as described above, according to national guidelines. Larvae investigations will be conducted by provincial staff at least 1 day before and 1 day after source reduction to determine the intervention effectiveness, and again 3 weeks post-intervention to determine the sustainability of intervention measures.