Development and Validation of the BELIEF Scale: A Theory-Integrated Measure of Hepatitis B Vaccination Motivation Among Health Sciences Students in Vietnam

Background Health sciences students are at increased occupational risk of hepatitis B virus infection due to early clinical exposure. Although vaccination is highly effective, uptake among healthcare trainees remains suboptimal. Existing studies often rely on ad hoc instruments and rarely integrate established behavioral theories within a validated measurement framework. This study aimed to develop and validate a theory-informed scale to assess motivational beliefs toward hepatitis B vaccination among Vietnamese health sciences students. Methods A cross-sectional instrument development and validation study was conducted among undergraduate health sciences students at a large medical university in Vietnam. Item generation was theory-driven, integrating constructs from the Health Belief Model and Protection Motivation Theory, and followed COSMIN recommendations for scale development. Content validity was assessed by expert review. Structural validity was examined using exploratory and confirmatory factor analyses. Internal consistency was evaluated using Cronbach’s alpha and composite reliability, while convergent and discriminant validity were assessed using average variance extracted and the Fornell–Larcker criterion. Results A total of 1,633 students participated. Exploratory factor analysis supported an eight-factor structure, and confirmatory factor analysis demonstrated good model fit (χ²/df = 4.82; CFI = 0.95; TLI = 0.94; RMSEA = 0.05). The final BELIEF-V30 scale showed high overall internal consistency (Cronbach’s α = 0.91). Subscale reliability ranged from 0.64 to 0.93, with lower values observed in constructs with fewer items. Convergent and discriminant validity were supported. Perceived susceptibility and perceived vulnerability converged into a unified risk appraisal construct. Conclusions The BELIEF scale is a psychometrically supported, theory-integrated instrument for assessing hepatitis B vaccination motivational beliefs among health sciences students. The scale is suitable for group-level research, educational evaluation, and public health intervention design in HBV-endemic settings.