Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 43 2 2005 04 15 79 84 A. Jafarzadeh S. M. A. Sajjadi 2015 09 28 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 Iranian children 5 years after primary vaccination and the response to a booster dose using recombinant hepatitis B vaccine. Totally, 81 children who had received primary course of hepatitis B vaccine at 0, 1.5 and 9 months of age were included in this study. A booster dose of hepatitis B vaccine was administered at 5 years after completion of primary vaccination program. Children were tested for anti-HBs antibody just before administration of booster dose and at 4 weeks after booster vaccination. An 81.5% seroprotection rate (anti-HBs > 10 IU/L) was observed 5 years after primary vaccination. After administration of booster dose, 100% of the children developed protective level of anti-HBs antibody and geometric mean titer rose from 206 IU/L to 1278 IU/L. These results indicate the existence of an effective immunological memory over a period of 5 years after primary vaccination with recombinant hepatitis B vaccine in healthy Iranian children. https://acta.tums.ac.ir/index.php/acta/article/view/2968 https://acta.tums.ac.ir/index.php/acta/article/download/2968/2949