Yeast derived hepatitis B vaccine in dental students. A three-year follow-up study

Sixty healthy adults (56 dental students and four post-graduates of the Dental Faculty in Milan; mean age 26.4 years, range 22-42 years) were vaccinated with a recombinant DNA vaccine (Engerix B, Smith Kline and French; 20 μg given i.m. at time 0, 1 and 6 months). One month after the third injection, 98.3% ( 59 60) vaccinees showed anti-HBs at levels higher than 10 mIU ml-1 (geometric mean titre 734.8 mIU ml-1). One year after the beginning of vaccination (i.e. 6 months after the third injection of vaccine), 46 vaccinees showed anti-HBs titre higher than 100 mIU ml-1 (24 between 100 and 1000 mIU ml-1 and 22 higher than 1000 mIU ml-1) and 14 vaccinees had anti-HBs below 100 mIU ml-1 (12 between 10 and 99 mIU ml-1 and 2 below 10 mIU ml-1). Since duration of antibody is directly related to the height of the initial response, the 14 vaccinees with lower anti-HBs titres were given a fourth dose of vaccine. All boosted vaccinees showed a vigorous anti-HBs response and the post-booster anti-HBs GMT increased to 1570 mIU ml-1 compared with 47.8 mIU ml-1 attained before the boosting injection. At three years from the beginning of vaccination, all vaccinees who showed anti-HBs titres higher than 100 mIU ml-1 after the primary vaccination and all but one of the boosted vaccinees were still anti-HBs positive. Our study indicates that a booster dose of vaccine given at 12 months to those vaccinees showing anti-HBs below 100 mIU ml-1 may be useful to elicit a more vigorous antibody production and hence to delay the decline in the protection afforded by the vaccine.