Nearly one in three Nigerian children aged 12-23 months (30.9%) has received no vaccinations at all, according to the 2024 Nigeria Demographic and Health Survey. This paper asks who these children are and why routine immunisation continues to miss them. It combines secondary analysis of the survey's published tables with qualitative evidence from the author's doctoral fieldwork among community members and World Health Organization staff in Nigeria. The survey shows that zero-dose children are concentrated in the North West (46.6%), in rural areas (40.4%), among children of mothers with no education (51.0%) and in the poorest households (49.1%); almost all children who never had a vaccination card (91.2%) are unvaccinated. The fieldwork shows communities contrasting door-to-door polio campaigns with under-resourced primary health care centres, and reading the contrast as a reason for suspicion. The paper argues that zero-dose children are a predictable outcome of decades of investment in vertical campaigns over the everyday health system, and that closing the gap requires rebuilding trust in primary health care, not further campaigns alone.