Geospatial inequalities in zero-dose vaccination and structural determinants: Insights from sub-Saharan Africa...

Zero-dose children-those who receive no routine vaccines-signal missed prevention and deep inequities. Sub-Saharan Africa (SSA) carries the largest zero-dose burden, yet pan-regional, subnational evidence on where these children live and which structural factors matter most remains limited.

We analysed Demographic and Health Surveys (DHS) from SSA (2015-2023). The primary outcome was "vaccine-never" (0-59 months) and antigen-specific zero-dose. Country-specific spatial heterogeneity was assessed using generalized additive models via the smooth's estimated degrees of freedom. Multivariable models (survey-weighted) quantified the associations between zero-dose vaccine and sociodemographic characteristics and their population-attributable risk percentages (PAR%) were estimated in multifactorial setting.

We included 179,971 children (0-59 months). Pooled zero-dose prevalence was 26 %; antigen-specific zero-dose was 43 % measles, 13 % BCG (bacille Calmette-Guérin), 18 % polio, 19 % DTP (Diphtheria-toxoid), 21 % tetanus. National zero-dose varied widely (∼10-11 % in Kenya/Zambia to ∼34-45 % in Angola/Madagascar), with marked within-country ranges (Angola 7-63 %). Most countries showed significant spatial heterogeneity, revealing localised "hotspots". In pooled models, rural residence, lowest wealth, lack of maternal schooling/literacy, and limited information access were strongly associated with zero-dose. Service-contact gradients were steep: home delivery and no/low antenatal care (ANC) showed large increases in odds, consistent with missed early contact. At population level, geolocation and deprivation/information blocks explained substantial burden (PAR%: 30-40 % for location/socioeconomic status (SES); 30-60 % for literacy/information, varying by country).

Zero-dose in SSA is highly clustered sub-nationally and tightly linked to structural disadvantage and weak early contact with the health system. By integrating individual, household, and spatial perspectives, this work aims to inform strategies for reducing inequities in immunisation and accelerating progress toward Immunisation Agenda (IA) 2030 targets.