Booster doses of hepatitis B vaccine: Responses to low-dose inoculations

Objective: To examine the anamnestic response to hepatitis B vaccine in previously vaccinated subjects. Design: Subjects who had received a course of hepatitis B vaccine at least two years previously had a sample of blood taken before and seven days after a low-dose booster of hepatitis B vaccine. Setting and participants: A pilot group of laboratory scientists in the Microbiologlcal Diagnostic Unit; fifth year medical students, University of Melbourne; and a group of ambulance officers from the Geelong Ambulance Depot (Victoria). All participants volunteered after having been informed of the study. Outcome measures: Serum levels of antibody to hepatitis B surface antigen (HBsAg) were measured before and after the booster dose of vaccine and, when available, in serum taken a month after the end of the primary course of vaccine, and the changes in antibody level were studied. Results: Although some individuals with a restricted antibody response were identified, most showed a quick response. There was limited evidence that this rise peaked early and began to fall within weeks. Conclusions: In many subjects, levels of antibody to HBsAg peak early after booster doses of vaccine but the rapid anamnestic response to small amounts of antigen make it probable that affective protection from symptomatic illness may be long lasting, when there has been a satisfactory primary response. This provides an argument for testing for adaquate seroconversion after vaccination.