Vaccination against influenza in patients with rheumatoid arthritis: the effect of rituximab on the humoral response

Objective: To assess the effect of rituximab on the efficacy and safety of influenza virus vaccine in patients with rheumatoid arthritis (RA). Methods: The study group comprised patients with RA treated with conventional disease-modifying drugs with or without rituximab. Split-virion inactivated vaccine containing 15 μg haemagglutinin/dose of B/Shanghai/361/02 (SHAN), A/New Caledonian/20/99 (NC) (H1N1) and A/California/7/04 (CAL) (H3N2) was used. Disease activity was assessed by the number of tender and swollen joints, duration of morning stiffness and evaluation of pain on the day of vaccination and 4 weeks later. CD19-positive cell levels were assessed in rituximab-treated patients. Haemagglutination inhibition (HI) antibodies were tested and response was defined as a greater than fourfold rise 4 weeks after vaccination or seroconversion in patients with a non-protective baseline level of antibodies (