Immune Response to Influenza Vaccine in Pediatric Patients With Inflammatory Bowel Disease

Background & Aims: The aim of this study was to compare response to inactivated influenza vaccine in healthy children and pediatric patients with inflammatory bowel disease (IBD). Methods: A prospective, open-label, controlled clinical trial during influenza seasons of 2002-2004 was performed. Single-dose inactive trivalent influenza vaccine was administered. Immune response to vaccination was measured by pre-immunization and postimmunization hemagglutinin inhibition titers. A postimmunization hemagglutinin inhibition titer of 40 or higher was considered protective against influenza. IBD activity and adverse events were recorded. Results: Eighty subjects were enrolled (29 healthy controls, 51 IBD patients). One patient did not complete the study. Patients were divided into 3 subgroups: infliximab and immunomodulatory (16), immunomodulatory (20), and anti-inflammatory therapy (14). Immunomodulatory therapy included corticosteroids, 6-mercaptopurine, or methotrexate. Overall, there was a statistically significant decrease in immune response in patients compared with healthy controls who received 1 influenza vaccine antigen (B/Hong Kong, P = .0125). Patients receiving infliximab and immunomodulatory therapy were less likely to respond to 2 influenza vaccine antigens (A/New Caledonia/20/99 and B/Hong Kong/330/2001, P = .018 and .0002, respectively). Fifteen subjects (19%) reported 19 mild adverse events: 11 (14%) reported soreness at the site, 4 (5%) reported having a cold, 3 (4%) reported flu-like symptoms, and 1 (1%) reported a headache. The clinical activity of IBD was not affected by vaccination. Conclusions: The serologic conversion rate to influenza vaccine in patients with IBD ranged from 33% to 85%. Patients on concomitant infliximab and immunomodulatory therapy are at risk of inadequate response to vaccination. The vaccine was safe and did not affect IBD activity.