Evaluation of anti-HBs seropositivity rates in children with familial mediterranean fever

The aim of this study was to evaluate and compare anti-HBs seroprotection rates and antibody titers in pediatric familial Mediterranean fever (FMF) patients to healthy controls. This cross-sectional, single-center study included FMF patients followed at a tertiary pediatric rheumatology center between August 2016 and August 2024. Only patients who had received HBV vaccination according to the national vaccination schedule and had priorly documented anti-hepatitis B surface antibody (anti-HBs) titers were included. Anti-HBs levels >  = 10 mIU/mL were considered seroprotective against HBV. A healthy control group, matched by age and gender with FMF patients included for comparison. FMF patients were categorized as colchicine-resistant and colchicine-responsive FMF patients. A total of 153 FMF patients and 158 healthy controls were included. FMF patients exhibited significantly lower anti-HBs seroprotection rates (46.4% vs. 58.2%; p = 0.037) and lower median anti-HBs titers (8.5 mIU/mL [IQR, 2–49.5] vs. 20.1 mIU/mL [IQR, 2–107.5]; p = 0.013) compared to healthy controls. Among FMF patients, males showed higher seroprotection rates (n = 44, 55.7%) compared to females (n = 27, 36.5%) (p = 0.017). In the FMF group, anti-HBs seroprotection rates declined with increasing age, from 75% in the youngest cohort (< 8 years) to 41.7% in adolescents (15–18 years) (p = 0.022). The seroprotective anti-HBs rate was significantly lower in colchicine-resistant FMF patients (n = 32, 45.1%) compared to the control group (n = 92, 58.2%) (p = 0.04). None of the patients tested positive for HBsAg, and no new HBV infections developed during a median follow-up of 67 months (IQR, 36–76).  Conclusion: Children with FMF demonstrated lower anti-HBs titers and seroprotection rates compared to healthy controls. Colchicine resistance, older age, and female gender were associated with lower seroprotectivity. Serological screening for HBV immunity in FMF patients may help to guide individualized vaccination strategies.