Immunogenicity of low doses of recombinant hepatitis B vaccine in young males

A trial of low doses (1.25 and 0.625 micrograms) of recombinant hepatitis B vaccine in 110 males aged 17-19 years is reported. Follow-up was extended to one year and further data are reported for participants from earlier trials of 10, 5 and 2.5 microgram doses for comparison. Seroconversion rates after the booster dose were 94% at 1.25 micrograms and 89% at 0.625 micrograms, compared to 100% at higher doses. Geometric mean titres (GMT) of antibody to hepatitis B surface antigen (anti-HBs) were significantly lower with the 0.625 microgram dose than with 1.25 micrograms at all times, reaching a GMT of 42.6 IU l-1 and 152.9 l-1, respectively, after the booster dose. GMT values at 12 months were 513.9, 510.0, 320.7, 46.5 and 13.3 IU l-1 in the 10, 5, 2.5, 1.25 and 0.625 microgram dose groups, respectively. Increases in GMT after the booster dose were parallelled in all groups. GMT decreased by approximately equal to 65% between 7 and 12 months in the three lowest dose groups, significantly less than the fall of 80% at 5 and 10 micrograms. However, to secure variability among vaccinees, the minimum effective dose for young adults should be greater than 5 micrograms per dose.