Explanatory factors for dropping out of the immunization schedule for children aged 0-11 months in Kinshasa: Cox regression model

Abstract

The persistence of vaccine-preventable diseases in urban African settings, particularly in Kinshasa, highlights an insufficient control of the determinants of immunization dropout despite the well-established effectiveness of vaccination programs. However, few local studies have applied robust analytical approaches, especially survival models, to quantify both the risk and timing of dropout, thereby revealing an important scientific gap. This study aims to identify the explanatory factors associated with immunization schedule dropout among children aged 0 to 11 months in Kinshasa. A retrospective case-control analytical study was conducted, supported by a cluster survey, involving 292 participants (146 cases and 146 controls). Data were collected using a structured questionnaire administered to caregivers and analyzed using Cox regression to estimate hazard ratios. The results indicate that children in the case group had a significantly higher risk of dropout (HR = 2.53; 95% CI: 1.84–3.47). Low household income (<1 USD/day) increased this risk by 84% (HR = 1.84; 95% CI: 1.26–2.69), while belonging to the central vaccination catchment area increased the risk by 93% (HR = 1.93; 95% CI: 1.39–2.70). Parental lack of education emerged as the most influential factor (HR = 6.04; 95% CI: 4.19–8.69). Additionally, high proportions of dropout were observed among children of illiterate mothers (89.6%), those living in Masina I health zone (45.2%), and those from low-income households (30.6%). In contrast, distance to the vaccination site was not significantly associated with dropout. These findings indicate that immunization dropout in Kinshasa is primarily driven by socio-economic, educational, and organizational factors, underscoring the need to strengthen targeted community-based interventions and improve household living conditions to enhance adherence to vaccination programs.