Despite high measles vaccine coverage, sub-Saharan Africa still has outbreaks, especially in fragile children. This study examined the measles vaccine's immunogenicity in HIV-positive and HIV-negative children aged 2–15 in Lusaka, Zambia. All 200 children, 100 HIV-positive and 100 HIV-negative, had received at least two doses of measles-containing vaccination and had no recent measles infection. Bayesian regression with integrated nested Laplace approximation was used to analyse socio-demographic, dietary, clinical, and immunisation histories, and ELISA was used to quantify measles-specific IgG titres. Spatial clusters of non-retained immunity were identified using QGIS. The results showed 49.5% of children lacked protective IgG. Significantly reduced odds of maintained immunity were linked to HIV infection, age ≥10 years, co-infections, and lack of breastfeeding. GIS study found non-retained immunity hotspots in Chawama and Kanyama sub-districts, which are densely populated and have poor healthcare access. Breastfeeding increased immunity retention, supporting worldwide maternal antibody transfer literature. This study illuminates Zambia's immunological measles protection gaps in at-risk groups. Targeted booster vaccination for older and HIV-infected children, integration of immunisation services into ART clinics, and GIS-supported surveillance to guide fair vaccine administration are recommended. These findings suggest policy realignment to prioritise high-risk communities with data-driven, context-specific immunisation initiatives. The study shows the utility of Bayesian and GIS methods in public health epidemiology and sets a precedent for resource-limited immunisation research. Measles, HIV, IgG, Zambia, Bayesian INLA, GIS, breastfeeding, public health policy.