Duration of Protection From Pneumonia After Pneumococcal Vaccination in Hemodialysis Patients

The investigators compare two strata of vaccinated patients: those recently vaccinated and those vaccinated more than two years ago. The primary objective is to compare pneumonia rates between the groups. As exploratory objectives, the investigators will describe the anti-pneumococcal antibody titers in hemodialysis patients as a function of time since vaccination, and determine factors influencing antibody kinetics. Further exploratory objectives investigate the relationship between antibody titers and the incidence of pneumonia in hemodialysis patients and extrapolate a possible cut-off for protection from pneumonia.