An Original Ecological Analysis of the Geographic Clustering of Vaccine-Preventable Disease Outbreaks in Nigeria

Vaccine-preventable disease outbreaks in Nigeria exhibit geographically clustered patterns that reflect the intersection of immunisation programme weaknesses, ecological determinants, conflict disruption, and population immunity gaps in ways that conventional surveillance analysis fails to systematically characterise. This study conducted an original ecological analysis of geographic clustering of VPD outbreaks in Nigeria over a ten-year period. A spatial epidemiology and ecological analysis methodology was employed, using nationwide VPD outbreak data from the IDSR system, NCDC outbreak database, and WHO outbreak verified database for 2014 to 2023. Disease conditions included measles, meningococcal meningitis, yellow fever, pertussis, and circulating vaccine-derived poliovirus. Geographic cluster analysis used Kulldorff spatial scan statistics, SaTScan software, and Global Moran's I for spatial autocorrelation assessment. Ecological correlates of cluster membership including LGA-level immunisation coverage, population density, conflict intensity scores, healthcare facility density, and poverty index were assessed using negative binomial spatial regression. Results showed significant spatial clustering for all five VPDs, with persistent high-risk clusters concentrated in the North West and North East zones for measles and cerebrospinal meningitis and the North Central zone for yellow fever. Immunisation coverage below 50 percent was the strongest ecological correlate of cluster membership across all VPDs (IRR 3.8; p < 0.001). Conflict intensity showed significant interaction with immunisation coverage, amplifying outbreak risk in already low-coverage areas. The study provides an original spatial epidemiological characterisation of VPD outbreak geography in Nigeria, identifying priority LGAs for intensified immunisation and surveillance investments. Keywords: vaccine-preventable diseases, spatial clustering, ecological analysis, Nigeria, outbreak epidemiology