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P229. Kinetics of the Anti-HBs titers after vaccination against hepatitis B virus (HBV) in patients with inflammatory bowel disease (IBD)

M. Chaparro, A. Rodríguez-Nogueiras, J. Villagrasa, J.P. Gisbert

Hospital de la Princesa, Madrid, Spain

Background: Vaccination against HBV is now recommended and adequate response to the vaccine might be confirmed among IBD patients. As time passes, anti-HBs titers frequently become undetectable in immunocompromised populations. Among immunocompromised patients who respond to the vaccine, clinically significant HBV infection has been documented in those who do not maintain anti-HBs concentrations of ≥10 mIU/ml, which has been established as proctective titers.

Objectives: To understand the kinetics of the reduction of the anti-HBs titers over time in IBD patients who have responded initially to the vaccination. To identify predictive factors of reduction/negativization of anti-HBs titers in these patients.

Methods: Patients from our IBD Unit with anti-HBs >10 UI/l after HBV vaccination were prospectively included. Vaccination protocol consisted on the administration of double dose of Engerix B® at 0, 1 and 2 months. Anti-HBs titers were measured 2 months after the last vaccine dose administration. Patients with anti-HBs 10 UI/l after the first or the second vaccination attempts were considered for the subsequent follow-up, and anti-HBs titers at that moment were considered as basals ones. On these patients, anti-HBs titers were measured at 6 and 12 months after the basal determination. When anti-HBs titers were lower than 10 UI/l during the follow-up, they were considered negatives titers. Long-term maintenance of positive anti-HBs titers was estimated using Kaplan–Meier curves. Cox-regression analysis was performed to identify potential predictive factors for losing of anti-HBs protective titers.

Results: Thirty-eight patients were included (median age was 41 years, 50% were male and 76% had Crohn's disease). Seventy-nine percent of patients were under immunossuppresive treatment (37% on thiopurines, 26% on anti-TNF drugs and 16% with both of them). Fifteen patients (39%) had received two vaccination attempts. Basal anti-HBs titers were >100 UI/l in 82% of patients. The incidence rate of negativization of the anti-HBs titers was 62% per patient-year. The cumulative incidence of negativization of the anti-HBs titers was 27% after 6 moths and 57% after 12 months from the basal determination. Anti-HBs basal titers were statistically significant lower among patients who had negative values thereafter during the follow-up, compared with patients who maintained them over 10 UI/l (241 UI/l vs. 519 UI/l, p = 0.01). In the multivatiate analysis, neither the patient's age, gender, type of IBD or the treatment with thiopurines were associated with a higher probability of negativization of anti-HBs titers. The treatment with anti-TNF drugs was the only factor associated with a higher risk of negativization of anti-HBs titers (HR = 3.3, 95%CI = 1.2–9.3, p = 0.02).

Conclusions: (1) A high proportion of IBD patients with protective anti-HBs titers after vaccination lose them over time (2/3 of patients per year of follow-up). (2) The risk of losing protective anti-HBs titers is three-fold higher among IBD patients on anti-TNF therapy.