ABSTRACT
The efficacy of the COVID-19 mRNA vaccine, including the third vaccination in pediatric inflammatory bowel disease (PIBD) patients is not fully understood. This study aimed to evaluate the humoral immunogenicity of the BNT162b2 vaccine and the changes in durability until 20-28 weeks after the initial vaccine series in PIBD patients on immunosuppressive drugs. The safety of the initial vaccine series and the booster effect of the third vaccination were also evaluated. A single-center, prospective cohort study was conducted, and 63 participants (anti-TNFα: 11; non-anti-TNFα: 31; 5-ASA: 21), with a mean age of 15.2 (range 9.6-17.9) years, were enrolled. All PIBD patients were seroconverted, with no serious short-term AEs. PIBD patients on anti-TNFα had significantly lower antibody titers than those on other medications at all measurement points. Furthermore, antibody titers waned over time with anti-TNFα and were significantly lower at 20-28 weeks than at 3-9 weeks after a two-vaccine series. In all 10 patients (anti-TNFα: 5; non-anti-TNFα including 5-ASA: 5), the third vaccination led to antibody concentrations significantly higher than those at the same time point after the second vaccination. PIBD patients on anti-TNFα need to remain vigilant about COVID-19 even after two vaccinations, and a third vaccination may be considered.