This project is a case study that uses a sequential explanatory mixed methods design to examine big catch-up (BCU) implementation in Bauchi and Rivers states, Nigeria, and to generate evidence on catch-up vaccination strategies and lessons learned. The case study seeks to document and analyze how BCU activities were planned, implemented, and monitored, examine approaches for establishing and institutionalizing catch-up vaccination within routine immunization and primary health care services, and understand factors influencing the existence of children not reached by vaccination.
