Japanese Encephalitis Vaccine Decision Aid for Travelers: A Randomized Clinical Trial.

Importance: Japanese encephalitis (JE) is a mosquito-borne disease with low infection risk but high consequences. Low uptake of JE vaccines among travelers persists despite effective vaccines. Tools that improve decision quality may help address this gap. Objective: To evaluate whether a web-based JE vaccine decision aid (JEVaDA) improves decision-making and vaccine uptake among Australian travelers compared with an online government JE resource. Design, Setting, and Participants: This parallel-group, single-blind randomized clinical trial was conducted online across Australia from November 6, 2024, to July 14, 2025. Adults (aged ≥18 years) planning travel to a JE-endemic country within 6 months were recruited via a research panel. Interventions: Participants were randomized 1:1 to the JEVaDA intervention, developed to International Patient Decision Aid Standards, or an online government JE resource (the active comparator). Main Outcomes and Measures: The primary outcome was postintervention decisional conflict, measured using the Decisional Conflict Scale (DCS) (scores range from 0 to 100, with higher scores indicating greater conflict). Secondary outcomes included change in JE knowledge, intention to vaccinate, and self-reported vaccine uptake. Analyses used regression models adjusted for baseline values, age, and gender. Results: Of the 1879 individuals screened, 814 were randomized and 769 completed preintervention and postintervention assessments (modified intention-to-treat population: 373 in the intervention group and 396 in the comparator group). Their mean (SD) age was 44.7 (15.2) years; 394 (51.2%) identified as women. The intervention and comparator groups showed significant reductions in decisional conflict (mean DCS score change, -10.94 [95% CI, -12.81 to -9.07] vs -11.58 [-13.24 to -9.91] points, respectively; both P < .001), with no between-group difference (β, -0.87 [95% CI, -2.93 to 1.19]; P = .41). JE knowledge improved in both groups (intervention vs comparator: 2.27 [95% CI, 2.00-2.54] vs 2.63 [95% CI, 2.36-2.91] correct responses; P < .001), with no between-group difference (incidence rate ratio [IRR], 0.95 [95% CI, 0.90-1.00]; P = .07). Positive change in intention to vaccinate occurred in 72 participants (19.3% [95% CI, 1.53%-2.33%]) in the intervention group vs 66 (16.7% [95% CI, 1.30%-2.04%]) in the comparator group (adjusted odds ratio [AOR], 1.19 [95% CI, 0.80-1.76]; P = .40). Among the 348 travelers completing follow-up after travel to JE risk areas, vaccine uptake was 35.1% overall (n = 122) and was significantly higher in the intervention group than in the comparator group (69 of 161 [42.9%] vs 53 of 187 [28.3%]; AOR, 2.22 [95% CI, 1.36-3.61]; P = .001). Conclusions and Relevance: In this randomized clinical trial, the web-based JEVaDA was not associated with a further reduction in decisional conflict compared with an active comparator but was associated with higher vaccine uptake. These findings suggest that decision aids can support informed, values-congruent choices in complex, preference-sensitive health decisions such as travel vaccination and beyond. Trial Registration: anzctr.org.au Identifier: ACTRN12624001176550.