Immunization continuity failures and measles vaccine dropout in a fragile urban setting: Evidence from Mogadishu, Somalia.

Objectives: Persistent measles transmission in fragile and conflict-affected settings is often linked to failure to complete multi-dose childhood immunization schedules. This study aimed to examine immunization completion and measles vaccine dropout to assess continuity of routine immunization services among children aged 12-23 months in Hodan District, Mogadishu, Somalia. Study design: Community-based cross-sectional study. Methods: A community-based cross-sectional study was conducted between May and July 2025 among 270 caregivers of children aged 12-23 months selected using multistage cluster sampling. Vaccination status was verified using immunization cards and caregiver recall. Vaccine coverage, full immunization status, and dropout rates between successive doses were calculated. Bivariate and multivariable logistic regression analyses were performed to explore factors associated with incomplete vaccination (p ≤ 0.05). Results: Full immunization coverage was 45.2% (95% CI: 39.3-51.2), with 54.8% of children incompletely vaccinated. Coverage declined across successive vaccine doses, from 75.9% for BCG to 55.9% for Penta3 and OPV3. Measles first-dose coverage was 46.3%, decreasing to 27.0% for the second dose, resulting in a high dropout rate of 41.6%. Maternal education, antenatal care attendance, immunization advice, and caregiver knowledge were associated with incomplete vaccination in bivariate analysis; however, no independent predictors remained significant after multivariable adjustment. Conclusions: Substantial immunization dropout following vaccine initiation indicates important continuity gaps within routine immunization services in this urban fragile setting. Strengthening follow-up mechanisms, caregiver communication, and defaulter-tracking systems may improve vaccine completion and reduce measles outbreak risk.