SUMMARYPatients receiving haemodialysis are at an increased risk of hepatitis B infection; regular screening for incident infection and vaccination of susceptible individuals is recommended. Haemodialysis patients often require repeated high-dose hepatitis B vaccination boosters because of impaired response. Since the hepatitis B surface antigen is used as an immunogenic agent for vaccination and as a marker of hepatitis B infection, it has occasionally been detected in the blood shortly after vaccine administration and can be mistaken for a new infection. These transient results, however, are unlikely to persist for longer than 14 days after vaccination. We report the case of a haemodialysis patient who tested weakly positive for hepatitis B surface antigen 52 days after a vaccine booster. This is the longest vaccineinduced antigenaemia described in the literature and indicates that vaccination can cause weakly positive hepatitis B surface antigen results for longer than previously reported. BACKGROUND