Nigeria's National Program on Immunization provides free life-saving vaccines to children, significantly reducing the risk of vaccine-preventable diseases. Despite improvements in immunization uptake, gaps persist, particularly among zero-dose children who have not received any routine vaccines. Factors contributing to this issue include insecurity, poor access to healthcare, vaccine hesitancy, and financing problems. Immunization services are funded through collective efforts of federal, state, and local governments, but challenges like delayed fund releases and overdependence on donor funds hinder progress. Recent initiatives, such as the Nigeria's Strategy for Immunization and PHC System Strengthening and the Nigerian Health Sector Renewal Investment Program, aim to enhance immunization coverage and health outcomes. A budget analysis across four states—Bauchi, Borno, Kano, and Sokoto—highlights the need for improved coordination, timely fund disbursement, and targeted advocacy to address the gaps in reaching zero-dose children and under-immunized populations.