Bayesian spatial analysis of child vaccination coverage and associated determinants in Tanzania

Childhood immunisation is one of the most effective public health interventions, significantly reducing morbidity and mortality from vaccine-preventable diseases. Despite global efforts, many low-income and middle-income countries, including Tanzania, face challenges in achieving high vaccination coverage. This study examined the spatial distribution and determinants of full vaccination coverage among children aged 12-23 months in Tanzania.

A cross-sectional design was applied using 2022 Tanzania Demographic and Health Survey-Malaria Indicator Survey data, including 2143 children aged 12-23 months. Spatial dependence was analysed with Moran's I and Local Indicators of Spatial Association to detect clustering. A Bayesian spatial hierarchical logistic regression, specified with the Besag-York-Mollié model and fitted via Integrated Nested Laplace Approximation, assessed individual and community-level determinants of vaccination coverage.

The findings showed that only 54.6% of children were fully vaccinated, which is below the national target and the 90% threshold recommended by the World Health Organization (WHO). Maternal education, antenatal care (ANC) attendance and household wealth were significant predictors of full vaccination. Children of mothers with higher education had higher odds of being fully vaccinated (OR=3.78; 95% CI 1.38 to 12.2), and those whose mothers attended four or more ANC visits were more likely to be fully vaccinated (OR=1.24; 95% CI 0.97 to 1.59). Children from middle-income households also had increased odds (OR=1.39; 95% CI 1.04 to 1.85). Maternal age and place of delivery were not statistically significant. Spatial analysis revealed significant geographic clustering of vaccination coverage (Global Moran's I=0.229, p=0.028), with high-coverage clusters in Kusini Unguja, Kigoma, Mara and Njombe, and low-coverage clusters in Songwe, Rukwa and Shinyanga.

The study highlights the importance of enhancing maternal education, strengthening ANC counselling, reducing financial and access barriers and implementing region-specific interventions to improve childhood immunisation coverage and reduce inequalities across Tanzania.