Vaccination against seasonal influenza is effective in Japanese patients with rheumatoid arthritis enrolled in a large observational cohort

OBJECTIVE: To investigate the effectiveness of influenza vaccination in patients with rheumatoid arthritis (RA) from a large practice-based cohort. METHOD: Patients with RA enrolled in the Institute of Rheumatology, Rheumatoid Arthritis (IORRA) cohort completed self-administered questionnaires as part of the April IORRA surveys of 2001, 2002, 2003, and 2007, which included their influenza vaccination status and occurrence of an actual influenza attack. Vaccine coverage rate and attack rates were calculated in each season. Relative risks (RRs) of vaccination for an actual influenza attack were evaluated and risk factors for influenza infection were determined by multiple logistic regression analysis. RESULTS: Data from 3529, 4518, 4816, and 4872 patients in the 2000/01, 2001/02, 2002/03, and 2006/07 seasons, respectively, were analysed. Coverage rates were increased from 12.2% in the 2000/01 season to 38.7% in the 2006/07 season. For each season, the attack rates in vaccinated patients trended lower than the rates in unvaccinated patients but the differences were not significant; however, by combining these four seasonal results, the attack rate was significantly lower for vaccinated patients [RR 0.83, 95% confidence interval (CI) 0.71-0.95, p < 0.01]. Male gender [odds ratio (OR) 1.48, 95% CI 1.25-1.76, p < 0.001] was associated with increased risk whereas vaccination was associated with reduced risk for influenza attack (OR 0.76, 95% CI 0.63-0.91, p < 0.01). There were no associations between influenza attacks and RA disease activity, treatment with methotrexate (MTX) or corticosteroids. CONCLUSION: Influenza vaccination was effective in patients with RA regardless of disease activity or treatment.