This study aimed to evaluate the impact of the COVID-19 pandemic on routine immunization (RI) programs in six Northern Nigerian states: Bauchi, Borno, Kaduna, Kano, Sokoto, and Yobe. This study compared the programmatic data of 2019 and 2020, as well as survey data collected during the pandemic. RI program variables included service delivery, leadership and governance, monitoring and evaluation/supportive supervision, community engagement, vaccine supply chain and logistics, and finance and financial management. Data were analyzed using SPSS (version 23, IBM), student t-test, and structural equation modelling. The results showed that RI programs were affected by the pandemic in terms of reduced meetings and low completion rates of action points in certain states. However, routine immunization support services increased owing to improved monitoring techniques and consistent vaccine deliveries, with fewer reports of stock-outs. The most significant impact of the pandemic was observed on activities coordinated at the healthcare facility level, whereas those at the state level were less impacted. The major challenges encountered during the pandemic included insufficient supplies and consumables, movement restrictions, shortage of human resources, and fear of infection.