Hepatitis B immunization has been offered to all grade 4 students (age 9-10) in the province of Quebec, using Engerix-B at a dose of 10 mkg. The peak incidence of hepatitis B occurs between age 15 and 35; the proportion of vaccinated children who will still be protected at this age is currently unknown. This study is designed to determine:

• persistence of immunity until age 25
• persistence of immunological memory as demonstrated by an anamnestic response following a booster dose
• the effect of a booster dose on immunogenicity at either 5, 10 or 15 years after the primary vaccination course (at age (15, 20 or 25).

Three doses of Engerix-B vaccine (10 mkg) were administered according to 0, 1, 6 month schedule to 1126 9-10 year-old children.

The primary objective of the study is to evaluate the persistence of antibodies to Engerix-B in all subjects at age 25 and to compare the levels obtained in those given a booster injection at age 15 or 20 with those receiving no booster injection.

Secondary objectives

• To determine the antibody levels obtained following primary vaccination and the proportion of children who seroconvert
• To determine the antibody levels of one third of subjects at age 15, 5 years after primary vaccination (Group A)
• To determine the effect on antibody levels of a booster injection at age 15 years given to one third of the subjects (Group A)
• To determine the antibody levels of subjects in groups A and B at age 20, 5 years after booster (Group A), 10 years after primary vaccination (Group B)
• To determine the effect on antibody levels of a booster injection at age 20 years given to one third of the subjects (Group B)
• To determine the effect on antibody levels of a booster injection at age 25 years given to one third of the subjects (Group C)
• To determine the antibody levels of subjects in Group A and Group B one year after their 5 or 10 year booster
• To evaluate safety

Inclusion Criteria:

• Previously completed the 1995 to 1996 Hepatitis B vaccination program vaccinations (Primary study) to the best of his/her knowledge and already enrolled and followed in the long term study
• Must be HBc negative
• Required standard interval between last dose of primary immunization and booster vaccination
• Written informed consent obtained from the subject
• Free of obvious health problems as established by medical history and clinical examination before entering into the study
• Previously completed routine childhood vaccination to the best of his/her knowledge
• If the subject is female, and the potential of pregnancy exists, it must be asked prior to immunization by the study nurse. According to the protocol d'immunisation du Québec, Engerix-B is not contra-indicated during pregnancy. However, if a participant thinks she could be pregnant (sexually active and no oral contraception or intra uterine device), a pregnancy test will be carried out. In case of pregnancy, the booster vaccination will be performed after delivery.

Exclusion Criteria:

- Not applicable