Determinants of diphtheria vaccination uptake during a mass immunization campaign in Mogadishu, Somalia: a cross-sectional study.

Background: Diphtheria has re-emerged as a major public health threat in fragile and conflict-affected settings, where routine immunization systems are disrupted. Outbreak response vaccination campaigns are critical for rapid disease control; however, evidence of post-campaign vaccine uptake and its determinants among internally displaced populations remains limited. This study assessed diphtheria vaccination uptake and associated socio-demographic, behavioral, and communication-related factors following a mass immunization campaign in an internally displaced person (IDP) camp in Mogadishu, Somalia. Methods: A community-based cross-sectional post-campaign survey was conducted with 384 caregivers residing in an IDP camp in Mogadishu. Data were collected using a structured interviewer-administered questionnaire implemented in KoboToolbox. Variables included caregiver characteristics, household income, diphtheria awareness, exposure to campaign phone messaging, and behavioral and social drivers of vaccinations. Descriptive statistics and multivariable logistic regression analyses were performed to identify the factors independently associated with campaign vaccination uptake. Results: Overall, 57.6% of children reported receiving diphtheria vaccination during the campaign. After adjustment, higher vaccine safety concern scores were independently associated with lower odds of vaccination (adjusted odds ratio [AOR], 0.72; 95% CI: 0.57-0.90). Caregivers with primary education had lower odds of vaccinating their children than those with no formal education (AOR = 0.36; 95% CI: 0.14-0.93). Inverse associations were observed for prior diphtheria awareness and the receipt of phone-based messages, likely reflecting targeted outreach to households with unvaccinated children rather than deterrent effects. Trust in health workers, perceived access, and social norms were not independently associated with uptake. Conclusion: Diphtheria vaccination coverage following an outbreak response campaign in an IDP setting was suboptimal. Vaccine safety concerns have emerged as the primary modifiable barrier to uptake, underscoring the need for safety-focused risk communication and strengthened interpersonal counseling during emergency immunization efforts in fragile and displacement-affected contexts.