A growing number of patients with Crohn's disease are treated with immunosuppressive agents, such as anti-tumor necrosis factor blockers and immunomodulators. Several recent studies have indicated that immunosuppressive treatment may impair the immunological response to pneumococcal vaccination in patients with inflammatory bowel disease (Crohn's disease and Ulcerative colitis). One of weaknesses in the previous studies did not focus on specific disease, such as Crohn's disease. In addition, predictive factors affecting impaired response following pneumococcal vaccination have not clearly evaluated in patients with Crohn's disease. In this study, patients with Crohn's disease will be assessed for serological response to pneumococcal vaccination. Further, potential predictive factors that impact on vaccination outcomes and adverse events related to vaccination will be evaluated.