Immunogenicity and safety of a plasma-derived heat-inactivated hepatitis B vaccine (CLB): studies in volunteers at a low risk of infection with hepatitis B virus

The safety and immunogenicity of a plasma-derived heat-inactivated hepatitis B vaccine (CLB) were evaluated in 471 healthy human volunteers, who, both in their occupations and in their private lives, had been at minimal risk of being infected with hepatitis B virus. The first 202 individuals received three 3-micrograms doses of heat-inactivated hepatitis B surface antigen (HBsAg) at one-month intervals (trial A). A total of 42% one month after the first injection, 84% after two months, and 93% after five months had become anti-HBs (antibody to hepatitis B surface antigen) positive. In a second randomized study (trial B), the immunogenicity of five different dosages of the vaccine was compared in 269 volunteers. When the dose of HBsAg was diminished from 3 micrograms to 1.5, 0.6, and 0.25 microgram, no decrease of the anti-HBs response was observed. However, when the dose was diminished to 0.1 microgram of HBsAg, the anti-HBs response dropped significantly to 63% (p less than 0.001). In the recipients of all five vaccine dosages, no influence of sex and age was found on the anti-HBs conversion rates. During the eight-month observation period, none of the vaccinees became HBsAg and/or anti-HBc (antibody to hepatitis B core antigen) positive, and none developed antibodies associated with autoimmune liver disease. No serious side effects were observed.