Persistence of antibody level to hepatitis B vaccine among children: Survey after several years of mass vaccination

Introduction: In Mongolia, the initiation of a national hepatitis B virus (HBV) vaccination programme in neonates and infants in 1991 has greatly contributed to the prevention of HBV infection. Objective: The aims of the present study were to determine the long-term immunogenicity and the decay rate of HBV surface antibody (anti-HBs) from universal HBV vaccination in an area of hyperendemicity. Results: A total of 1,145 apparently healthy children (592 boys and 553 girls) who were vaccinated against HBV at infancy and monitored for anti-HBs at 7 to 12 years of age entered the study. Serum samples were analyzed for anti-HBs by chemiluminescence immunoassay and antibody titers were quantified in mIU/ml. Among children who produced antibodies, a slow decrease in the level of anti-HBs was observed; the proportion of children with vaccine induced anti-HBs levels (>/=10 mIU/mL) has been decreased by age from 31.1% to 16.6% between age of 7 and 12 years (p<0.01). The protective anti-HBs positive rates of children, who were received three, two, one doses of HBV vaccine in their infancy, were 22.0%, 14.3%, 8.7% (trend p<0.05), respectively. The mean geometric titre of anti-HBs was 45.8 mIU/mL, and no significant associations were observed with sex and residence. Conclusions: Vaccination against viral hepatitis B results in persistence of immune protection of the vaccine and retention of immune memory to HBV in the vast majority of the vaccinees even after 10 years. Complete doses of vaccines should be provided for infants to retain better immunity against HBV infection.