Miller Williams Afolabi2026-01-262026-01-262025-12kate TurabianP.hDhttps://repository.lcu.edu.ng/handle/123456789/1249Immunisation is the process through which an individual acquires immunity or resistance to an infectious disease, primarily by the injection of a vaccine. Vaccine-preventable diseases (VPDs) remain the predominant contributors to childhood mortality, resulting in around 3 million fatalities annually, predominantly in Africa and Asia. Worldwide, immunisation averts approximately 2-3 million fatalities among children under five years of age. This study assessed the factors associated with the uptake of childhood immunisation by mothers of under-five children in Ajeromi-Ifelodun Local Government Area, Lagos State. A cross-sectional descriptive survey design was used for this study while Fishers' calculation sampling technique was used to determine the sample size of 801 respondents that participated in the study. The instrument used in data collection was self-structure questionnaire which was administered to respondents, out of which 801 was completely filled, returned and analyzed, using Statistical Package for Social Sciences (SPSS) version 28.0 Results of data analyzed was presented in frequency count tables, percentages and charts. Findings of the study revealed that the largest proportion of respondents was aged 25-29 years, this falls within the reproductive age of women in sub-Saharan Africa of 15-45years and corresponds with the findings that the mean age of mothers at first birth in south-west, Nigeria was 24.4. Most of the babies (39.5%) were born in primary health care centres with only 1.1% at home. The respondents were mostly married. Also, most of their partners had good educational levels, with more than 50% having tertiary education. Percentage of completion is high for penta1, opv1 and pcv1 but ipv1 and rota1 had a lower completion. Which could be due to vaccine stock out. The next set of vaccines is taken at 10 weeks, vaccines like penta2, pcv2, and opv2 were mostly reported to be largely completed, while rota2 was not, this could be due to reasons like vaccine stock out, moithers forgetting the date of the vaccination or the requirement to pay before its administration. Also, it has been reported that payments are made in some facilities before the administration of vaccines even in public facilities. This could discourage immunisation uptake for their children. However, the trend of completion decreased afterwards with meningitis being the least with less than 50% completion, while vitamin A1 had the most completion of 98.3%. This result is consistent with reports that after 10 weeks there was a decreased uptake of immunisation. In conclusion, the findings indicate that maternal knowledge, attitudes, and perspectives regarding the paediatric Routine Immunisation (RI) program are predominantly satisfactory. Engagement in antenatal care, institutional delivery, and elevated educational levels were positively associated with a thorough understanding of the immunisation program and vaccine- preventable diseases (VPDs). Future initiatives are necessary to improve maternal awareness and address misconceptions that may impede vaccination coverage rates in Lagos and other Nigerian states. Health facilities ought to issue reminders to carers before the next routine immunisation to inform them of their child's forthcoming vaccination schedule. Keywords: immunisation, determinants, mothers, children, vaccine Word count:486enimmunisationdeterminantsmotherschildrenvaccineThesis