Factors associated with zero-dose status and caregiver opportunity costs among 12–23-month-olds in Mont Ngafula 1 Health Zone, DRC

Background Zero-dose prevalence, the proportion of children who have not received any routine immunisations, is a critical gauge of programme performance. In 2021, one area of Mont Ngafula 1 Health Zone (HZ) in Kinshasa, Democratic Republic of Congo, experienced consecutive months of 0% immunisation coverage, raising concerns about access and uptake. We aimed to determine the prevalence of zero-dose status among 12–23-month-old children in Mont Ngafula 1 HZ, identify associated factors, and explore caregivers’ and providers’ perspectives on vaccination barriers. Methods Between April and July 2024, we carried out a mixed-methods study among children aged 12–23 months in Mont Ngafula 1 HZ. A three-stage probability sample of 406 caregivers was selected. Quantitative data were collected via a structured questionnaire to calculate vaccination coverage and assess associations (χ² and logistic regression). Qualitative data were generated through focus group discussions and in-depth interviews with caregivers, community relays, and nurses. Transcripts were coded and thematically analysed. Results Vaccination coverage for the pentavalent series was 72%, leaving 28% (n = 112) of children zero-dose. On multivariable analysis, zero-dose status was independently associated with maternal age < 25 years (adjusted odds ratio, aOR 3; 95 % CI 1.2–7.6), low caregiver knowledge about vaccines and vaccine preventable diseases (VPD)s, and perceptions of direct and indirect costs of immunisation (p < 0.05). Qualitative findings corroborated these barriers, highlighting confusion over fee policies and mistrust between caregivers and health staff. Conclusions Despite free‐of‐charge immunisation policies, nearly one-third of eligible children in Mont Ngafula 1 HZ remain unvaccinated. Persistent knowledge gaps, cost misperceptions, and communication breakdowns undermine uptake. Strengthening community–health system partnerships, clarifying fee policies, and intensifying health education are essential to reduce zero-dose prevalence and improve child health outcomes.