Immunisation induces both antibody-producing-cells and memory cells. Although antibodies progressively decline over time, long-term follow-up studies of infants, children and adults vaccinated against hepatitis B have indicated that low or undetectable antibody responses years after vaccination are not associated to the development of chronic hepatitis. This is associated to the rapid development of anamnestic responses, reflecting persistence of hepatitis B memory cells. This resulted into a change of initial recommendations, which now highlight that booster doses are unnecessary in immunocompetent persons after a complete course of vaccination.