ABSTRACT
The aim of the present study was to identify the true extent of non-responsiveness in children vaccinated against Hepatitis B virus [HBV] ten years ago at birth whom were serologically susceptible to HBV,and had poor antibody response to booster HBV vaccine. Twenty low-and non-responding 11.5 years old children recuited in by another study received three additional doeses of HB vaccine 4-6 weeks apart. Anti-HbS antibody titers were assessed before and 4-6 weeks after each dose of vaccine by using ELISA method. All children showed anamnestic antibody responses after receiving the first additional dose of vaccine. There was no significant differences between the mean concentration of antibody after the first, second and third doses of vaccine. Study results showed that those children who did not respond to booster does of the HB vaccine may not be real non-responder.HB vaccine at infancy induces long-time immunologic memory which provides seroprotection by exposure to HBs-Ag