Prevalence and factors associated with polio vaccine failure among children aged 1–10 years in Maniema and Ituri, Democratic Republic of Congo: a cross-sectional survey

Background Polio remains a major public health concern in the Democratic Republic of Congo (DRC), which contributes nearly half of all circulating vaccine-derived poliovirus type 2 (cVDPV2) cases reported in Sub-Saharan Africa. Despite ongoing vaccination efforts, outbreaks continue to occur, including among vaccinated children. Maniema and Ituri provinces are among the most affected regions. This study assessed the prevalence and determinants of polio vaccine failure in these two provinces. Methods A cross-sectional study was conducted from February to April 2024 across Maniema and Ituri. A total of 408 children documented as fully vaccinated against polio were enrolled. Data on sociodemographic characteristics, anthropometry, and biological parameters were collected, and serological and biochemical markers were analysed. Prevalence ratios (PRs) were estimated using multivariable regression to identify factors associated with vaccine failure. Results The prevalence of polio vaccine failure was 50% in Maniema and 62% in Ituri. Independent predictors of vaccine failure included having a mother with no formal education (adjusted prevalence ratio, PR = 1.59; 95% CI: 1.08–2.12), lymphocytosis (adjusted PR = 1.85; 95% CI: 1.09–3.15), and monopenia (adjusted PR = 1.86; 95% CI: 1.11–3.17). Conversely, normal and high thrombocyte counts were associated with lower risk of vaccine failure (adjusted PR = 0.66; 95% CI: 0.50–0.87 and adjusted PR = 0.42; 95% CI: 0.26–0.66, respectively). Conclusions Polio vaccine failure is common in Maniema and Ituri and appears to be influenced not only by maternal education but also by haematological profiles of vaccinated children. These findings underscore the need for integrated approaches that consider biological vulnerability alongside social determinants to strengthen polio control strategies in the DRC.