Socioeconomic and health system determinants of zero-dose and under-immunization among children in Zambia: Evidence from the 2024 Demographic and Health Survey

Despite progress in childhood immunization, Zambia retains pockets of zero-dose children (those who have not received the first dose of diphtheria-tetanus-pertussis-containing vaccine, DTP1) and under-immunised children (those missing one or more vaccines in the recommended schedule), sustaining vulnerability to vaccine-preventable diseases. Understanding the factors associated with missed vaccination is essential for achieving Immunization Agenda 2030 targets. We analysed cross-sectional data from 1,738 children aged 12-23 months identified through the 2024 Zambia Demographic and Health Survey, a nationally representative survey using a stratified two-stage cluster sampling design. Three outcomes were assessed: zero-dose status (no DTP1), under-immunization by the basic schedule (BCG, DTP1-3, OPV1-3, measles-1), and under-immunization by the national expanded schedule (basic plus PCV1-3 and rotavirus1-2). Survey-weighted multivariable regression identified associated factors. Nationally, 3.2% (95% CI: 2.1-4.3%) of children were zero-dose, 36.1% (95% CI: 33.0-39.2%) were under-immunised by the basic schedule, and 69.9% (95% CI: 67.0-72.8%) by the national schedule. Zero-dose prevalence ranged tenfold across provinces, from 0.6% in Lusaka to 6.9% in North Western. In adjusted models, children in the richest households had 93% lower odds of zero-dose than the poorest (aOR 0.07, 95% CI: 0.02-0.29). Facility delivery reduced zero-dose by 68% (aOR 0.32, 95% CI: 0.15-0.69). For basic-schedule under-immunization, secondary education (aOR 0.50, 95% CI: 0.30-0.82; prevalence ratio 0.68) and vaccination card possession (aOR 0.24, 95% CI: 0.14-0.40; prevalence ratio 0.53) were associated with lower odds. Wealth effects differed significantly by residence for all outcomes (p < 0.001). Zero-dose and under-immunization in Zambia are profoundly socioeconomically and geographically patterned. Reaching zero-dose children requires targeting the poorest households and those with home deliveries, particularly in North Western and Northern provinces. Improving vaccination card coverage may reduce broader under-immunization. Gaps in national schedule coverage are consistent with supply-side constraints requiring structural health system responses, though direct supply-side measurement was beyond the scope of this analysis.