Beyond Individual Factors: Disentangling Context from Composition in Zero-Dose Children and the Three Delays to Vaccination in Sub-Saharan Africa

Background: Zero-dose children - those who have not received any routine vaccines - represent a critical challenge for achieving universal immunization coverage. This study applies the Three Delays Model to examine multilevel factors associated with zero-dose children in sub-Saharan Africa. Methods: We analyzed data from 59,211 children aged 12-23 months across 28 sub-Saharan African countries using Demographic and Health Surveys (2016-2021). Zero-dose status was defined as not receiving the first dose of diphtheria-tetanus-pertussis vaccine. Multilevel logistic regression models examined individual-, community-, and country-level determinants guided by the Three Delays Model framework. Results: The overall zero-dose prevalence was 10.71% (95% CI: 6.90-15.23), with substantial variation ranging from 0.43% in Rwanda to 42.29% in Chad. In the fully adjusted model, poor maternal health-seeking behavior showed the strongest association with zero-dose status (OR = 15.21, 95% CrI: 13.28-17.35). Maternal education demonstrated a clear gradient effect, with children of mothers having no formal education showing nearly doubled odds of being zero-dose (OR = 1.84, 95% CrI: 1.36-2.81). Maternal empowerment factors were significant, including lack of decision-making power (OR = 1.31, 95% CrI: 1.21-1.43) and no media access (OR = 1.28, 95% CrI: 1.18-1.39). Community illiteracy rates (OR = 1.11, 95% CrI: 1.08-1.14) and low country-level health expenditure (OR = 3.45, 95% CrI: 1.85-5.72) were associated with increased zero-dose prevalence. Substantial clustering persisted at community (42.0%) and country (19.1%) levels in the final model. Conclusions: Zero-dose children are concentrated among the most disadvantaged populations, with maternal health-seeking behavior serving as the strongest predictor. The substantial multilevel clustering and diverse determinants identified necessitate integrated interventions addressing individual empowerment, community capacity, and health system strengthening. The marked cross-country variation demonstrates that universal vaccination coverage is achievable but requires sustained commitment to addressing underlying social determinants of health inequity.