*2.2. Data Collection and Analysis, including Co-Creation Workshops* 2.2.1. Data Collection

The research team and additionally trained data collectors collected data for this study through semi-structured and open-ended in-depth interviews (IDIs), focus group discussions (FGDs; Nigeria only), and co-creation workshops. In Nigeria, FGDs were used instead of interviews at the community level, with caregivers and community members separately, to optimize time and resources. Interview and FGD guides reflected the analytical frameworks, and we adapted during implementation based on emerging insights. The teams also collected health facility data for common indicators of facility readiness and performance, as found in existing health facility surveys and immunization-specific supportive supervision checklists. While these quantitative data were later used to inform our project's intervention design, we did not include them in the analysis presented at co-creation workshops due to the rapid implementation timelines (1–2 weeks for data collection, analysis, and co-creation) of these qualitative studies; thus, we do not report them here.
