Persistence of anti-HBs antibody and immunological memory in children vaccinated with hepatitis B vaccine at birth.

BACKGROUND Vaccination with the hepatitis B surface antigen (HBsAg) induces protective levels of antibody (anti-HBs = 10 IU/L) in majority of vaccinees. It has been shown that the levels of anti-HBs antibody do wane after vaccination. The aim of this study was to evaluate the persistence of anti-HBs antibodies in healthy Iranian children at 10 years after primary vaccination and the response to a booster dose using recombinant hepatitis B vaccine. METHODS Blood samples were collected from 146 healthy 10-11 years old children who received primary course of Hepatitis B vaccine at 0, 1.5 and 9 months of age. The sera were tested for anti-HBs, antibody to Hepatitis B core antigen (anti-HBc) and HBsAg by ELISA technique. A single booster dose of recombinant hepatitis B vaccine was administered intramuscularly to a total of 94 children, whose anti-HBs antibody was less than 50 IU/L (70 children with anti-HBs < 10 IU/L and 24 subjects with anti-HBs 10-50 IU/L). The sera of children were re-tested for anti-HBs antibody levels at 4 weeks after booster vaccination. RESULTS At 10 years after primary vaccination 70/146 (47.9%) of children had protective levels of antibody with geometric mean titer (GMT) of 68.12 IU/ml. All children were negative for HBsAg, although anti-HBc antibody was positive in 11 (7.5%) of children. In the 94 subjects who received the booster dose the seroprotection and the GMT of anti-HBs antibody were 25.5% and 9.58 IU/L at pre-booster time and rose to 95.75% and 575.6 IU/L after the booster vaccination, respectively. Seroprotection rates and mean titer of antibody similarly expressed in males and females. CONCLUSION The results of present study showed that at 10 years after primary vaccination with recombinant HB vaccine, 47.9% of the children had protective levels of anti-HBs antibody. Moreover we have demonstrated an anamnestic response to booster vaccination that confirms the persistence of an effective immunological memory in vaccinees.