Of the 110 dentists who had presented seroconversion 50 days after the intradermal application of three 2 µg doses of the Belgian recombinant vaccine against hepatitis B (HB),
or latent HBV infection during the eight years following the first vaccination. A 2 µg booster dose was administered intradermally to eight dentists with anti-HBs titers lower than 10 mIU/ml (non-responders) and to six dentists with titers ranging from 10 to 100 mIU/ml (poor responders); the determination of anti-HBs one month later demonstrated the occurrence of seroconversion in the eight non-responders and an increase in anti-HBs titer in the six poor responders. In summary, the present results demonstrated the prolonged persistence of protection against HBV infection and the development of immunologic memory provided by vaccination against HB -with intradermal application of three 2 µg doses of the Belgian recombinant vaccine at 0, 1, and 6 months -carried out eight years before in 51 dentists.Key words: hepatitis B vaccine -seroconversion -immunologic memoryThe immunogenicity and safety of hepatitis B (HB) vaccines -both recombinant and derived from human plasma administered intramuscularly in three doses at standard intervals (0, 1, and 6 months) -are similar and have been widely confirmed (Szmuness et al. 1980, 1982, Stevens et al. 1985, Zajac et al. 1986, Lee et al. 1995. In addition to high seroprotection rates, several studies have demonstrated prolonged persistence of immunity against HB (Hadler et al. 1986, Stevens et al. 1985, Ding et al. 1993, Greenberg 1993, Lieming et al. 1993, Tabor et al. 1993, Wainwright et al. 1997, Wu et al. 1999, Dexter et al. 2002, Whittle et al. 2002 and the development of immunologic memory (Gonzalez et al. 1993, Lai et al. 1993, Resti et al. 1993, Trivello et al. 1995, West & Calandra 1996, Da Villa et al. 1997, Li et al. 1998, Shih et al. 1999 Banatvala et al. 2001, Watson et al. 2001, Dexter et al. 2002 as a result of the intramuscular application of both recombinant and human plasma-derived HB vaccines to adults and children using the scheme cited above. Banatvala et al. (2001) referred to four studies carried out with recombinant vaccines administered intramuscularly to adults and children using habitual doses and regimens, in which five to eight years after vaccination the serum anti-HBs titer was equal to or higher than 10 mIU/ml in 83% to 93% of the vaccinees. Watson et al. (2001), evaluating the response to intramuscular application of a booster dose of recombinant HB vaccine 13 years after the application of three usual doses at 0, 1, and 6 months, demonstrated the presence of immunologic memory in all individuals studied (18 vaccinated during childhood and seven vaccinated at more than 30 years of age).However, only few and short-term studies are available regarding the duration of immunity conferred by HB vaccine administered by the intradermal route. Thus, the objective of the present study was to determine the persistence of immunity conferred by recombinant HB vaccine administered in...