Persistence of anti-HBs and protective efficacy after administration of hepatitis B vaccine

To evaluate the effect of hepatitis B vaccine on the persistence of anti-HBs and its efficacy in preventing hepatitis type B, anti-HBs and anti-HBc levels were studied over a period of 5.5 years. Plasma-derived hepatitis B vaccine, containing 20 micrograms of HBsAg protein, was injected subcutaneously in 122 healthy medical staff members, followed by two identical injections 1 and 6 months later. Anti-HBs and anti-HBc levels were then measured by radio-immunoassay. The anti-HBs titres were expressed as the sample/negative (S/N) ratios, and an S/N ratio of more than 2.1 was considered positive. The mean (and s.d.) anti-HBs titre peaked 7 months after the first vaccination with an S/N ratio of 153.6 +/- 149.8, after which it decreased with time. The mean anti-HBs titre dropped to an S/N ratio of 8.0 +/- 5.1 5.5 years after the first vaccination. The percentage of vaccinees who were anti-HBs positive also gradually decreased with time after a peak of 84.2% at 7 months following the first vaccination. The percentage of vaccinees who were anti-HBs positive was 38.9% 5.5 years after the first vaccination. The anti-HBc level was not positive in all subjects during the observation period. Five vaccinated volunteers who had developed anti-HBs after the basic vaccination, but whose acquired antibody level became negative within 4.5 years following the first vaccination, were administered a booster dose of 20 micrograms of HBsAg 4.5 years after the first vaccination. Only one of these subjects did not respond to the booster vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)