RESUMO
Long-term protection against hepatitis B virus [HBV] is dependent on persistence of anti-HBs antibodies and/or strong immunological memory. In this study we evaluated the persistence of anti-HBs antibodies in healthy children aged 4-12 years after primary vaccination and the response to a booster dose using recombinant hepatitis B vaccine. Totally, 182 children who had received primary course of hepatitis B vaccine at 2, 4 and 6 months of age were included in this study. Anti-HBs levels were measured using enzyme-linked immunosorbent assay [ELISA] quantitative method to evaluate the immunogenecity of the vaccine. Children with anti-HBs levels < 10 m lU/ml were revaccinated with a pediatric dose of recombinant HB vaccine [0.5 ml: 10 microg] intramuscularly. After 4 weeks their anti-HBs levels were reevaluated to test the response. All children displayed an anamnestic antibody response when tested 4 weeks after the booster dose. The mean anti-HBs levels before and 4 weeks after injection were 2.8 and 108.7mlU/ml respectively. There was a significant negative correlation between age of the children and the prebooster antibody titre, while the age had no effect on the response of children to the booster vaccine. Other host related factors such as gender, BMI which could produce variability in immune response, showed no significant correlation with prebooster or anamnestic anti HBs response. In spite of declining levels of anti-HBs the subjects usually exhibit signs of well preserved B cell memory, they respond rapidly to a booster vaccination. Currently there is no reason to offer booster doses of hepatitis B vaccine within the first 12 years of age