The adult formulation of this combination hepatitis A-hepatitis B vaccine contains 720 enzyme-linked immunosorbent assay units (EU) of formalin-inactivated hepatitis A virus strain HM175 and 20mug of recombinant DNA yeast-derived hepatitis B surface antigen adsorbed onto aluminium salts in 1ml for injection. The paediatric formulation contains half this dosage in 0.5ml for injection. The combination vaccine has been shown to be highly immunogenic in healthy young adults after the full dosage schedule of 3 doses at 0, 1 and 6 months. Trials in older adults and children indicate that immunogenicity is adequate in these groups also. The immunogenicity of the combination vaccine appears to be similar to that of hepatitis A vaccine and hepatitis B vaccine administered separately. Possible advantages for the combination vaccine recipient include fewer injections and lower costs. Local adverse reactions such as soreness at the injection site, redness and swelling occur often with the first dose of the series, but the incidence falls with subsequent doses. Local reactions are usually mild and transient, and reported systemic reactions (fatigue, headache) are thought not to have a causal link with the vaccine.