Mapping the distribution of zero-dose children to assess the performance of vaccine delivery strategies and their relationships with measles incidence in Nigeria
Authors: Utazi C. Edson , Aheto Justice M. K. , Wigley Adelle , Tejedor-Garavito Natalia , Bonnie Amy , Nnanatu Christopher C. , Wagai John , Williams Cheryl , Setayesh Hamidreza , Tatem Andrew J. , Cutts Felicity T. 
Published: October 2022

Geographically precise identification and targeting of populations at risk of vaccine-preventable diseases has gained renewed attention within the global health community over the last few years. District level estimates of vaccination coverage and corresponding zero-dose prevalence constitute a potentially useful evidence base to evaluate the performance of vaccination strategies. These estimates are also valuable for identifying missed communities, hence enabling targeted interventions and better resource allocation. Here, we fit Bayesian geostatistical models to map the routine coverage of the first doses of diphtheria-tetanus-pertussis vaccine (DTP1) and measles-containing vaccine (MCV1) and corresponding zero-dose estimates at 1×1 km resolution and the district level using geospatial data sets. We also map MCV1 coverage before and after the 2019 measles vaccination campaign in the northern states to further explore variations in routine vaccine coverage and to evaluate the effectiveness of both routine immunization (RI) and campaigns in reaching zero-dose children. Additionally, we map the spatial distributions of reported measles cases during 2018 to 2020 and explore their relationships with MCV zero-dose prevalence to highlight the public health implications of varying performance of vaccination strategies across the country. Our analysis revealed strong similarities between the spatial distributions of DTP and MCV zero dose prevalence, with districts with the highest prevalence concentrated mostly in the northwest and the northeast, but also in other areas such as Lagos state and the Federal Capital Territory. Although the 2019 campaign reduced MCV zero-dose prevalence substantially in the north, pockets of vulnerabilities remained in areas that had among the highest prevalence prior to the campaign. Importantly, we found strong correlations between measles case counts and MCV RI zero-dose estimates, which provides a strong indication that measles incidence in the country is mostly affected by RI coverage. Our analyses reveal an urgent and highly significant need to strengthen the country’s RI program as a longer-term measure for disease control, whilst ensuring effective campaigns in the short term.

Highlights

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In 2018, about 8,883,931 and 12,566,478 children aged under 5 years old in Nigeria had not received routine DTP1 and MCV1, respectively.

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MCV and DTP zero-dose prevalence shared similar patterns, with highest prevalence districts concentrated in the northeast and northwest but also found elsewhere

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Measles incidence, though mitigated by campaigns, is related to subnational routine MCV1 coverage

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Residual zero-dose prevalence following vaccination campaigns should be analysed and reported

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Targeted campaigns or routine immunization interventions in higher zero-dose prevalence districts are needed to reduce disease risk