Implementing the Big Catch-Up to close immunization gaps and adjust systems for restoring vaccination coverage: lessons from five countries

Overview

This report synthesizes findings from mixed-methods case studies conducted in Cameroon, Nigeria, Pakistan, the United Republic of Tanzania and Yemen to examine implementation of the Big Catch-Up (BCU), a global initiative launched in 2023 by WHO, UNICEF, Gavi and partners to help countries recover immunization coverage lost during the COVID-19 pandemic and strengthen their capacity to identify and vaccinate zero-dose and underimmunized children. It analyses how countries planned, implemented and monitored catch-up activities across diverse epidemiological and operational settings, exploring the factors that facilitated or hindered progress, from community demand and service delivery to data systems, workforce capacity and policy implementation.

The document highlights how the BCU contributed to strengthening immunization systems while identifying challenges to sustaining progress. It examines opportunities to institutionalize catch-up vaccination within routine immunization and primary health care, emphasizing the importance of continued investment in health worker capacity, community engagement, information systems and adaptive programme management. The cross-country lessons presented are intended to inform governments and global partners working to strengthen equitable immunization systems and advance the Immunization Agenda 2030 goal of leaving no child behind.