Abstract
Background: Zero-dose children, operationalised as children who have not received the first dose of a diphtheria–tetanus–pertussis-containing vaccine (DTP1), signal failure of initial contact with routine immunisation services. We estimated zero-dose prevalence and examined associated inequalities among children aged 12–23 months in Lao PDR. Methods: We analysed data from the 2023 Lao Social Indicator Survey III (LSIS III). DTP1 receipt was classified from home-based records and caregiver recall. Analyses accounted for the complex survey design. Separate survey-weighted logistic regression models used a prespecified core adjustment set. We assessed outcome availability and extreme-case prevalence bounds. Results: Of 1,876 age-eligible children, 1,509 had classifiable DTP1 status. Weighted zero-dose prevalence among classifiable children was 12.8% (95% CI 10.6–15.4); the extreme-case range among all eligible children was 10.4–29.2%. DTP1 status was unclassifiable for 19.6% and was disproportionately unavailable among dis-advantaged groups. Adjusted odds ratios (aORs) were higher for children in the Central than Northern region (aOR 3.96, 95% CI 2.31–6.80), and among Mon-Khmer-headed (aOR 2.72, 95% CI 1.51–4.89) and Hmong-Mien-headed households (aOR 3.48, 95% CI 1.82–6.63) than Lao-Tai-headed households. Children whose mothers had no formal education had higher adjusted odds than children whose mothers had secondary education or higher (aOR 2.09, 95% CI 1.18–3.68). Conclusions: Geographic, ethnolinguistic and ed-ucational inequalities characterised zero-dose status. The findings support locally tailored investigation, culturally and linguistically appropriate engagement, community identi-fication of zero-dose children, integration with maternal and child health services, and improved vaccination documentation.