Background: Immunization is the most cost effective public health intervention geared towards reducing childhood morbidity and mortality. There has been global increase in the rate of immunization coverage with its attendant decline in vaccine preventable deaths. The immunization coverage in developing countries like Nigeria, has however being challenging due to some reasons. Therefore, this study determined the immunization status and the factors affecting the vaccination status of under five children in Nasarawa State. Methods: Cross sectional descriptive studies of under five children in Nasarawa State using a multi staged sampling technique. Interviewer administered questionnaire was used for the recruited participants across the three senatorial zones of the state. Data collection was done using both the immunization cards and oral interview of care-givers. Data analysis was with the Statistical Package for Social Sciences (SPSS). Univariates, bivariates and multivariates analyses were done with significant value set at p < 0.05. Results: A total of 55,036 of the target population of 74,775 (4% of the total population of Nasarawa State) received (Baccille, Calmette and Guerin BCG) vaccine in the state in the year 2018, giving a 73.6% immunization coverage for Nasarawa State in the year 2018. Immunization drop – out rate for pentavalent vaccine was 31.6%. The location of Primary Healthcare Centre, antenatal care attendance, distance to healthcare centre and numbers of children in a household are strong determinants of the immunization status across Nasarawa State. Conclusions: There is high immunization coverage in the present study. Incomplete immunization is influenced by Ignorance, mother’s travelling, fathers refusal, child’s small stature and or illness as well as distance to the health facilities.

Keywords: Coverage, Determinants, Immunization, Status, Under five