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All subjects in this clinical study gave informed written consent, and guidelines of the authors' institution regarding human experimentation were observed in the conduct of the study. A booster dose of vaccine given to 18 adolescents (immunized as children) and 7 older adults immunized 13 years earlier with a 3-dose course of recombinant hepatitis B vaccine induced a strong secondary antibody response, demonstrating that the vaccinees retained immunologic memory for HbsAG. Within one week, booster vaccination induced an 11 to 24-fold rise in the GMT of anti-HBs which continued, reaching 52 to 319-fold after 4 weeks. Significantly even the 5 individuals with less than 10 mIU/ml of anti-HBs prior to the booster all had impressive responses to the booster dose.

Universal immunization of infants is essential to the control of hepatitis B in areas of high endemicity where infection commonly occurs in infants and children. It is also an attractive strategy for ultimately reducing hepatitis-B-associated acute and chronic liver disease in areas of lower endemicity where infections occur primarily in adolescents and adults. Integration of hepatitis B vaccine with other routine paediatric immunizations, using flexible scheduling, will enhance compliance while minimizing the need for additional resources. Clinical studies demonstrate that a very high proportion of healthy infants and adults develop a protective level of antibody when given hepatitis B vaccine using a wide range of schedules. Compliance with universal vaccination of infants against hepatitis B may be enhanced by the development of new combination vaccines (e.g. diphtheria-tetanus-pertussis-Haemophilus influenzae b-hepatitis B) that allow complete immunization against several antigens with a minimal number of injections.

One hundred and four healthy, hepatitis B virus (HBV) seronegative males were enrolled in a single blind, randomized pilot study to compare antibody and clinical responses to a yeast recombinant pre-S2 + S vaccine and a yeast recombinant S antigen vaccine (Recombivax HBR). Participants received either a 12, 24 or 48 micrograms dose of pre-S2 + S vaccine (with a 1:5 ratio by weight of pre-S2 and S antigens) or a 10 micrograms dose of Recombivax HBR by intramuscular injection at 0, 1 and 6 months; their serological and biochemical responses were measured at 0, 1, 2, 3, 6 and 7 months, while their clinical responses were monitored for 5 days after each injection. The proportion of vaccines with minor local or systemic complaints (mainly sore arm, malaise, myalgia, fatigue) and the proportion developing antibody to surface antigen (anti-HBs) were similar for all vaccine groups. Transient elevations in alanine aminotransferase occurred infrequently. By 7 months almost all vaccinees developed anti-HBs, but titres were generally higher among recipients of pre-S2 + S vaccine. Antibody to pre-S2 antigen developed in 70-75% by 2 months and in 91-96% by 7 months. These data imply that the recombinant yeast pre-S2 + S vaccine is as well tolerated and as immunogenic as Recombivax HBR. Further studies are being conducted to assess antibody responses in larger numbers of healthy adults as well as in special populations with sub-optimal responses to currently licensed hepatitis B vaccines.