Research in Medicine

Background The duration of infantile hepatitis B vaccination-induced immunity is still unknown. We assessed antibody persistence and immunological memory to hepatitis B 18 years after vaccination during infancy in Iranian young adults at risk of hepatitis B virus infection due to behavioral or occupational exposures. Methods This study was conducted on 395 freshman students of with a history of 3 times infant HB vaccination (10 µg recombinant HBV vaccine) 18 years ego (in accordance with the national vaccination program). Antibody against HBs Ag (anti-HBs) was measured and participants who had a serum protection (anti-HBs ≥ 10 mIu/mL) excluded. The others (anti-HBs < 10 mIu/mL) were given a booster dose (20 µg recombinant HBV vaccine) and the immune response was evaluated 10 to 14 days after injection. Increased antibody titer (≥ 10 mIu/mL) was considered as an enhanced response (anamnestic response) which is suggestive for immunological memory. Results Anti-HBs seropositivity rate was 79.2% (n=313). 42 of 82 seronegative participants received a booster dose and anamnestic response observed in 92.9% (n=39). After the booster dose geometric mean (GMCs) and range of anti-HBs antibodies were 216.8 and 1084.3 respectively (n=42). The mean antibody concentration was significantly different after the boost than before (3.07±1.37 vs. 517.97±435.75, p=0.000). Conclusion These findings show that the infantile HBV immunization induced a long-term protection in our group and immunological memory retained for at least 18 years.