Medical students are frequently at risk of being infected by hepatitis B virus (HBV) via occupational exposure to infected blood or body fluids. In 2002, the Faculty of Medicine Siriraj Hospital provided screening tests for HBV serology to all medical students for a vaccination campaign against the infection. There were 1,165 medical students tested. Eight hundred and eleven (69.6%) students had immunity by previous vaccination, but more importantly 212 (18.2%) had no immunity and required vaccination. Most of the students who needed to be vaccinated were in the pre-clinical year (82.5%). Moreover, the students in the pre-clinical year who had previous vaccination had a 2.2 times greater risk of having negative anti-HBs than the students in the clinical year (OR = 2.2, 95%CI = 1.4-3.5). This is because they might have been vaccinated when they were young and the antibody waned overtime.

Keywords: Medical students, Hepatitis B vaccination, Booster, Thai