Co-designing water sanitation and hygiene (WASH) messages for a social and behaviour change campaign in Kiribati.

Objectives: To examine sanitation behaviours, barriers and motivators in South Tarawa, and to assess how formative research, message pretesting and co-design processes can generate culturally resonant Social and Behaviour Change (SBC) messages for WASH programming in Pacific Island contexts. Study design: Rapid Assessment and Response (RAR) mixed-methods study. Methods: Data were collected through semi-structured interviews with 12 key informants and eight focus group discussions with community members (N = 73) across seven intervention villages. Co-design of message concepts and brand stimuli was integrated into focus groups, supported by quantitative ratings of message impact using a Smiley Face scale. Qualitative data were analysed using a hybrid Grounded Theory and Thematic Analysis approach, while quantitative differences across demographic groups were examined using ANOVA, t-tests, Chi-square and Fisher's exact tests. Results: Four organising themes and 22 subthemes were identified. Key barriers included entrenched social norms supporting open defecation, overcrowding, limited and poorly maintained sanitation infrastructure, and safety concerns for women and vulnerable groups. Participants preferred empowering narratives delivered by trusted opinion leaders, while humorous brand concepts reduced stigma around sanitation topics. Quantitative ratings confirmed the Leaders narrative and Sit-Wipe-Flush brand as the strongest performers. Conclusions: Embedding co-design within formative SBC research produced culturally grounded insights into sanitation behaviour change in South Tarawa. Findings highlight the need for phased message rollout aligned with infrastructure availability and demonstrate the value of participatory design approaches to enhance relevance, ownership and long-term effectiveness of WASH SBC interventions in Pacific Island and other LMIC settings.