Evaluation of HBsAb titre in adolescents 15-17 years after Hepatitis B vaccine administration

Abstract

Egypt is considered as a region of intermediate prevalence for HBV infection with reported figure of 4.5%. Infection with HBV in infancy or early childhood may lead to a high rate of persistent infection (25–90%), while the rates are lower if infection occurs during adulthood (5–10%). In most endemic areas, infection occurs mainly during early childhood and mother-to-infant transmission accounts for approximately 50% of the chronic infection cases. Neonatal HBV vaccination is the most effective measure for prevention of HBV infection in countries with intermediate to high levels of HBV endemicity. A compulsory vaccination programme against hepatitis B infection among infants was started in Egypt in 1992 using a yeast recombinant DNA vaccine (10 μg) and with a schedule of 2, 4 and 6 months of age. Vaccine efficacy (defined as HBsAbs concentration of ≥10 mIU/ml) is greatest in infants, children and young adults with protective antibody levels achieved in 95% of those vaccinated. Serologic studies have shown that the titer of antibodies against hepatitis B surface antigen drops within the first few years after vaccination and that one-third to one half of children vaccinated as infants will have titers below 10 IU/mL by 10–15 years of age. Up to our knowledge our study is the first to study the immune status to HBV vaccine among Egyptian children more than 15 years after primary immunization. Our study was conducted on two hundred twenty five (225) healthy junior students; 16-18 years old who received full hepatitis B virus vaccination course according to Egyptian Expanded Immunizing Protocol (EEIP) during first year of life. Serum hepatitis B surface antibody titer was done using ELISA. Antibody level was determined quantitatively by means of a standard curve calibrated against the World Health Organization reference preparation. Anti-HBs titres were expressed in IU/ml. Anti-HBs ≥10 IU/ml was considered according to international standards to be protective against HB infection. The seroprotection at 15-17 years after immunization was (8.9%) 20 of 225 students had HBsAbs ≥10 IU/ml. There were no statistically significant differences between males and females, also there were no statistically significant differences by socioeconomic status or residency place. A booster dose of the HBV vaccine was given to 56 (25%) of the studied students whose HBsAbs was less than 10 IU/ml and serum HBsAbs level measured after one month, 100% of them showed positive anamnestic reaction with increase of HBsAbs level ≥ 10 IU/ml.