Background: Although Egypt had adopted implementation of routine infant hepatitis B virus (HBV) vaccination in 1992, its effectiveness is not evaluated on a national scale. Assessment of early and long-term seroprotection after compulsory vaccination is an important measure for monitoring the success of the vaccination program.
Aim: The aim of this study was to assess HBV seroprotection and immune memory in children and adolescents who were vaccinated during infancy in Cairo Governorate.
Materials and methods: The study was carried out in two phases. The first phase was a cross-sectional study carried out in five districts in Cairo Governorate, recruiting 819 children in the age range of 9 months to 16 years. All children had received full doses of the compulsory HBV vaccination. Serum samples were taken from each child and assessed for antibody against hepatitis B virus surface antigen (anti-HBs) titer; total antibodies against HBV core antigen, and HBV surface antigen. HBV DNA was investigated by real-time PCR for those who were HBV core antigen or HBV surface antigen positive. In the second phase, nonseroprotected children (anti-HBs <10 IU/I) received HBV booster dose. AntiHBs titer was reassessed after 4 weeks to identify anamnestic response. Individuals showing antibody concentrations ofless than 10 IU/l were then given an additional complete course of vaccination.
Results: Four out of 819 children had HBV breakthrough infection. The seroprotection rate was 60.7%, and was significantly higher among children aged less than 5 years compared to the older age groups and among boys compared to girls. Multivariate logistic analysis showed age as the only independent predictor of low anti-HBs titer. About 95% of nonseroprotected children developed anamnestic response postbooster. Anti-HBs geometric mean titer (GMT) increased significantly from pre-booster (13.8±16.9IU/L) compared to post-booster (307±6.0IU/L, P<0.001). Anti-HBs GMT was significantly higher among children with prebooster anti-HBs level ≥1 IU/l (424.9±4.4 IU/l) compared to children with undetectable level (178.3±8.3).
Conclusion: Despite waning of anti-HBs over time, long-term protection still exists. The high anamnestic response rate signifies the existence of immune memory and giving a booster dose is not recommended. However, we suggest that prolonged follow up and surveillance of vaccinees immunized at an early age should be continued.
Keywords: Booster; Vaccination; hepatitis B virus; hepatitis B virus surface antigen; seroprotection.