Spatial clustering of measles vaccination coverage among children in sub-Saharan Africa

Abstract

Background: During the past two decades, vaccination programs have greatly reduced global morbidity and mortality due to measles, but recently this progress has stalled. Even in countries that report high vaccination coverage rates, transmission has continued, particularly in spatially clustered subpopulations with low vaccination coverage.

Methods: We examined the spatial heterogeneity of measles vaccination coverage among children aged 12-23 months in ten Sub-Saharan African countries. We used the Anselin Local Moran's I to estimate clustering of vaccination coverage based on data from Demographic and Health Surveys conducted between 2008 and 2013. We also examined the role of sociodemographic factors to explain clustering of low vaccination.

Results: We detected 477 spatial clusters with low vaccination coverage, many of which were located in countries with relatively high nationwide vaccination coverage rates such as Zambia and Malawi. We also found clusters in border areas with transient populations. Clustering of low vaccination coverage was related to low health education and limited access to healthcare.

Conclusions: Systematically monitoring clustered populations with low vaccination coverage can inform supplemental immunization activities and strengthen elimination programs. Metrics of spatial heterogeneity should be used routinely to determine the success of immunization programs and the risk of disease persistence.

Keywords: Africa; MCV; Measles; Spatial analysis; Spatial heterogeneity; Spatial regression.

Fig. 1

Vaccination coverage and DHS clusters in the study area. The location of each DHS cluster is depicted as a grey circle. We computed the average vaccination coverage rate for each country from DHS cluster-level data. Both maps were created by study investigators using open access data sources

Fig. 2

Spatial clustering of vaccination coverage in DHS clusters. Using the Anselin Local Moran’s I, we classified each DHS cluster as being part of a spatial cluster with low-vaccination, high-vaccination, or mixed vaccination coverage (low-vaccination near high-vaccination or vice versa). Grey circles indicate that vaccination coverage for a DHS cluster was not statistically significantly clustered. a We detected clustering of low, mixed, and high vaccination coverage in all countries. Vaccination coverage in some spatial clusters contrasted nationwide vaccination coverage rates: e.g., b in the Zanzibar/Pemba islands and the Kenya-Tanzania border population (low vaccination vs. high nationwide); c in Northern Malawi (low vaccination vs. high nationwide); and (d) in the Madagascar capital region (high vaccination vs. low nationwide)