Process evaluation of a migrant-inclusive risk communication and community engagement intervention: lessons from the Health Handbook for Vietnamese Workers in Japan

Background Migrant workers in Japan face persistent barriers to accessing timely and culturally appropriate health information owing to language constraints, complex administrative systems, and fragmented risk communication channels. These challenges were exacerbated during the COVID-19 pandemic, highlighting the need for migrant-inclusive risk communication and community engagement (RCCE). In response, the Government of Viet Nam, the International Organization for Migration (IOM), and Japanese partners collaboratively developed the Health Handbook for Vietnamese Workers in Japan as a transnational RCCE intervention. Methods This study presents a process evaluation of the development, dissemination, and adaptation of the Handbook. Multiple data sources were triangulated, including mixed-methods situation analyses, technical working group documentation, Patient Education Materials Assessment Tool (PEMAT) evaluations, digital analytics, and qualitative stakeholder feedback. Data were analysed using inductive thematic analysis informed by the RCCE principles and a social determinant of the health framework to identify the key mechanisms shaping intervention effectiveness. Results The evaluation identified three interrelated mechanisms that appeared to support migrant-inclusive RCCE: (1) addressing structural vulnerabilities; (2) deploying multichannel communication strategies tailored to migrants; and (3) engaging migrant communities and stakeholders. The Handbook provided practical and actionable health information, particularly on occupational health, healthcare navigation, and rights-related topics. Digital analytics demonstrated an increased reach following collaboration with community-based platforms, while the PEMAT assessment indicated high understandability (81.3%) but moderate actionability (66.7%), informing iterative revisions. The intervention also strengthened multisectoral collaboration and enabled continuity of health messaging across the migration cycle. Conclusions This study demonstrates that migrant-inclusive RCCE, when implemented through participatory, multisectoral, and transnational approaches, can enhance equitable access to health information and contribute to health system resilience. Institutionalizing such approaches within national preparedness frameworks is essential to ensure effective emergency responses and to address the structural determinants that shape migrant health.