Completeness of MMR Vaccination and Durability of Vaccine-Induced Antibody Responses in Children with Inflammatory Bowel Disease

Background: Children with IBD are at increased risk of suboptimal maintenance of vaccine-induced immunity, particularly when the MMR vaccination course is incomplete before diagnosis and initiation of immunosuppressive therapy. We conducted a prospective study to evaluate the durability of antibody responses to measles, mumps, and rubella in pediatric IBD patients and to determine how completeness of MMR vaccination influences long-term antibody persistence over 12 months. Methods: Sixty children with IBD were included. Demographic characteristics, clinical disease activity (PUCAI/PCDAI), inflammatory markers (CRP, ESR), and fecal calprotectin were extracted from electronic medical records. Vaccination completeness was ascertained from documented immunization history. Serum antibodies to measles, rubella, and mumps were measured at baseline and after 12 months. Seroprotection was defined using standard laboratory thresholds. Antibody decay over time was assessed with paired non-parametric tests, and time to loss of seroprotection was analyzed using Cox proportional hazards models. In addition, Bayesian ANOVA modeling was applied to quantify evidence for differences in antibody concentrations and decay kinetics according to vaccination status. Results: Overall, 66.7% of patients had completed the full MMR vaccination course. At baseline, seroprotection rates were 48.3% for measles, 76.7% for rubella, and 70% for mumps. After 12 months, median antibody concentrations declined significantly for all three antigens. Corresponding seroprotection rates changed to 46.7% for measles (p = 0.414), 70% for rubella (p = 0.046), and 66.7% for mumps (p = 0.157). Incomplete MMR vaccination was identified as a major modifiable risk factor for accelerated antibody waning in children with IBD. Cox regression demonstrated that incompletely vaccinated patients had a 2.13-fold higher risk of losing measles seroprotection (95% CI 1.07–4.24; p = 0.032), a 5.27-fold higher risk for rubella (95% CI 1.86–14.95; p = 0.002), and a 4.82-fold higher risk for mumps (95% Cl 1.68–13.85; p = 0.004). Bayesian analyses provided decisive evidence that vaccination completeness strongly influences baseline antibody levels. Conclusions: Incomplete MMR vaccination is associated with markedly reduced durability of vaccine-induced immunity to measles, mumps, and rubella in children with IBD. These findings underscore the need for systematic prevaccination screening, timely completion of age-appropriate vaccination before initiation of immunosuppressive therapy when feasible, and individualized serological monitoring to identify patients at highest risk of vaccine-preventable infections.