Low level of seroconversion after a novel influenza A/H1N1/2009 vaccination in Japanese patients with rheumatoid arthritis in the 2009 season.

We examined change in the antibody titre against pandemic influenza A/H1N1/2009 before and after vaccination in Japanese patients with rheumatoid arthritis. This observational study was conducted with the participation of five hospitals in Japan. A total of 89 patients with rheumatoid arthritis were included in this study. The seroprotection and seroresponse rates to vaccination with the pandemic influenza A/H1N1/2009 vaccine were analysed. The seroprotection rates prior to the vaccination were 5.6% in the Japanese patients with rheumatoid arthritis. The seroprotection rates after subcutaneous vaccination were 55.1%. The seroresponse rate after subcutaneous vaccination was 50.6% in the patients with rheumatoid arthritis. Both the seroprotection and seroresponse rates obtained after the vaccination with the pandemic influenza A/H1N1/2009 vaccine were low in Japanese patients with rheumatoid arthritis. We should realise that a vaccination against this newly emerged influenza virus may protect only half of the Japanese patients with rheumatoid arthritis in a real world.