Vaccination Against Influenza in Rheumatoid Arthritis Patients: The Effect of Rituximab on the Humoral Response

The study population comprised RA patients treated with conventional disease modifying drugs with or without rituximab. Split-virion inactivated vaccine containing 15 mcg hemagglutinin/dose of B/Shanghai/361/02 (SHAN), A/New Caledonia A/New Caledonia/ 20/99 (NC) (H1N1) and A/California/7/04 (CAL) (H3N2) was used. Disease activity was assessed by number of tender and swollen joints, morning stiffness duration, and evaluation of pain on the day of vaccination and 4 weeks later. CD20 positive cell levels were assessed in rituximab treated patients. Hemagglutination inhibition (HI) antibodies were tested and response was defined as >4-fold rise 4 weeks post vaccination or seroconversion in patients with a non-protective baseline level of antibodies (<1/40). Geometric mean titers (GMT) were calculated in all subjects.

Results: The participants were divided into 3 groups: RA (n=29, aged 64±12 years), rituximab-treated RA (n=14, aged 53±15 years) and healthy controls (n=21, aged 58±15 years). All baseline protective levels of HI antibodies and GMT were similar. Four weeks after vaccination, there was a significant increase in GMT for NC and California antigens in all subjects, but not for the Shanghai antigen in the rituximab group. Similarly, the percentage of responders was low for Shanghai and NC, but significantly lowers in rituximab treated patients for the California antigen compared with the other groups. Parameters of disease activity remained unchanged.

Conclusion: Influenza virus vaccine generated a humoral response in all RA study patients and controls. Although the response was significantly lower among rituximab-treated patients,