Immunogenicity of a reduced dose of recombinant hepatitis B vaccine

We report a trial of a reduced dose (2.5 micrograms) of recombinant hepatitis B vaccine, carried out over seven months in 54 males aged 17 to 19 years. Response to the reduced dose was significantly inferior to that found in equivalent trials of 5 and 10 micrograms doses. Although all seroconverted, three participants (6%) remained below the protective level of 10 IU l-1 of antibody to hepatitis B surface antigen (anti-HBs) and a further eight (15%) below 100 IU l-1, possibly requiring early revaccination. The final geometric mean titre of anti-HBs was 810 IU l-1 (95% confidence interval, 433 to 1520). It appears that 2.5 micrograms may be too low a dosage for general use in adults.