Applying Human-Centered Design and Iterative Programming to Identify and Reach Zero-Dose and Under-Immunized Children in Kenya: Lessons from the Zero-Dose Learning Agenda

Background Despite decades of investment in immunization, an estimated 14.3 million children worldwide remain zero-dose (ZD). Kenya's national coverage of approximately 72% masks significant subnational disparities, with existing methods failing to capture the context-specific drivers of zero-dose status. Objective: To apply human centered design (HCD) and continuous learning to understand Who are ZD children, Why they are ZD and to co-design and pilot tailored interventions in two high-burden Kenyan sub-counties. Methods We implemented the Zero Dose Learning Agenda in Turkana Central (rural, nomadic) and Rachuonyo North (semi urban) between November 2023 and December 2025. We applied PATHs Living Labs 4D HCD methodology (Discover, Define, Dream, Design) to guide the data collection process (interviews, observations, focus group discussions [FGDs], facilitated discussions), analysis (quantitative surveys, qualitative and data triangulation), co-creation/ideation (ideation, concept validation), prototyping (detailed concept sheet development, measurement and implementation plans) and iterative testing of three ZD interventions in select facilities and communities. Results We engaged 798 participants and identified six distinct caregiver archetypes per site. Gender norms dominated drivers in Rachuonyo North; geographic access and marginalization dominated in Turkana Central. Chanjo Talks Kazini (n=188) achieved 60.1% completion and 92.5% satisfaction; perceived spousal support increased from 37.1% to 74.4%. Quality Household Assessment and Sensitization trained 68 community health promoters, reached 874 households, and identified 15 zero dose and 39 under-immunized children, all subsequently vaccinated. Chanjo Mashinani conducted 30 low cost outreach events, reached 266 zero dose children, and reduced costs by over 70% versus conventional outreach. Iterative adaptation uncovered barriers including male caregivers' fear of HIV testing, invisible to baseline instruments. Conclusion Combining human-centered design with continuous learning enables immunization programs to diagnose context-specific barriers and correct course in real time. Zero-dose children share a label but not pathways to exclusion; effective reach requires tailored strategies that account for local gender dynamics, health system trust, and access constraints. Teaser key message ZD and UI children require tailored approaches and interventions to be identified, understood and reached, all while ensuring local voices engagement are not left at problem identification, and resources are availed to support weaker health systems.