BACKGROUND: The 2009 pandemic of influenza A (H1N1) prompted an urgent worldwide vaccination campaign, especially of high-risk subjects, such as maintenance haemodialysis (HD) patients. Still the immunogenicity of the pandemic A (H1N1) vaccine in HD patients is unknown. METHODS: We prospectively studied the immunogenicity of a monovalent adjuvanted influenza A/California/2009 (H1N1) vaccine (Pandemrix, GSK Biologicals, Rixensart, Belgium) in HD patients and controls. Antibody level was measured using a seroneutralization assay before (D(0)) and 30 days after (D(30)) a single 3.75 mug vaccine dose. Specimens were tested in quadruplicates. Geometric mean (GM) antibody titers were determined in each subject at D(0) and D(30). Seroconversion was defined as an increase in GM titers by a factor 4 or more. RESULTS: Fifty-three adult HD patients [aged 71 +/- 10, 58.5% males, on HD for a median of 38 (3 - 146) months] and 32 control subjects (aged 47.3 +/- 14, 31.3% males) were analyzed. Baseline GM titers were similar in HD patients and controls [7.9 (6.6 - 9.6) vs 10 (6 - 17); p = 0.69]. Seroconversion was observed in 30 (93.8%) controls and 34 (64.2%) HD patients (p = 0.002). In addition, GM titers at D(30) were significantly higher in controls than in HD patients [373 (