Despite the “Decade of Vaccines” in Africa, Nigeria continues to experience low routine immunization coverage, accounting for the highest number of unimmunized children globally. In 2017, over 4.3 million Nigerian children remained unimmunized, representing more than a quarter of all unimmunized children worldwide. Routine immunization coverage in Nigeria fluctuated between 33% and 54% from 2013 to 2017, with Kaduna State performing below the national average at 30%. Factors contributing to incomplete vaccination include lack of caregiver education, service delivery challenges, mistrust, and family constraints. In response, routine immunization was declared a public health emergency in 2017, with the establishment of coordination centers at national, state, and local levels. Strategic interventions implemented in Kaduna State—such as fixed and outreach services, optimized routine immunization supportive supervision, and periodic intensification campaigns—have gradually improved coverage from 45% in late 2017 to 73% in late 2018. These findings underscore the need for sustained, targeted strategies to reduce missed opportunities and improve equitable access to routine immunization in Nigeria.