Immunogenicity and safety of low doses of recombinant yeast-derived hepatitis B vaccine.

The immunogenicity and safety of recombinant yeast-derived hepatitis B vaccine given in doses of 0.6 microgram, 1.25 microgram, 2.5 micrograms and 5.0 micrograms were studied in 4 comparable groups of children aged 1-12 years. All children received three doses of vaccine at time 0, 1 month and 5 months. Immunogenicity appeared to be satisfactory in all 4 groups of children. In the early phase of the study, a dose-response relationship was observed but there was no significant difference in the geometric mean titre among all 4 groups for any period studied. Antibody levels peaked at 9 months, declining thereafter. The geometric mean titre one year after the first vaccine dose was not significantly lower than that at the peak (9 months) in any individual group studied. The second year geometric mean titre was similar in all 4 groups and lower than that of the first year. Sero-conversion with antibody titres greater than or equal to 10 mIU/ml was 100% in the 5.0 micrograms group and greater than 90% in the other 3 groups. There were no adverse reactions of any significance. The immunogenicity of recombinant yeast-derived hepatitis B vaccine was found to be adequate even at as low a dosage as 0.6 microgram when administered in a 3-dose regimen.