Four-year experience with a recombinant hepatitis B vaccine.

Three hundred and forty-three healthy adults were vaccinated with five different lots of recombinant hepatitis B vaccine. Three hundred and forty (99.1%) individuals produced antibodies against hepatitis B surface antigen (anti-HBs). Peak anti-HBs concentrations were significantly higher in females and younger individuals. All anti-HBs positive individuals developed antibodies to the common determinant "a" of HBsAg. The vaccine was well tolerated, without severe side reactions. Persistence of anti-HBs was followed in 130 individuals for 3, and in 15 for 4 years after the first vaccination of these two groups. 21.7% and 32.3%, respectively, no longer had protective levels of anti-HBs after this time. The persistence of anti-HBs was dependent on peak anti-HBs levels, with consistent kinetics of anti-HBs decline. Revaccination of individuals whose specific antibody levels had fallen below 10 IU/l led to a prompt anti-HBs response. Comparison with individuals vaccinated with plasma-derived hepatitis B vaccine revealed no substantial differences between the two vaccines.