Humoral Immune Memory to Hepatitis B Vaccine after Primary Vaccination of Children and Adolescents in Assiut, Egypt.

Objectives: We sought to assess the prevalence of hepatitis B virus (HBV) seroprotection among vaccinated children in the Assiut governorate, Egypt, and assess a booster dose immune memory response among non-seroprotected children.

Methods: Using a multistage cluster sample, 566 children were recruited from three clusters: one urban and two rural. Children were aged from nine months to 16 years old. All participants received the full three doses of the compulsory HBV vaccine during infancy. Serum hepatitis B surface antigen (HBsAg), total anti-hepatitis B core (anti-HBc) antibodies, and quantitative detection of anti-HBs were measured using enzyme-linked immunosorbent assay. Repeatedly positive samples for HBsAg/anti-HBc were submitted for quantitative HBV DNA detection using real-time polymerase chain reaction. Non-seroprotective participants (anti-HBs < 10 IU/L) were given a booster dose of HBV vaccine. Two weeks later, a blood sample was taken from each child to assess an anamnestic response.

Results: The seroprotection rate was 53.2%, and only two children had HBV breakthrough infection (0.4%) with positive serum anti-HBc and HBV DNA. Age was the only significant predictor for non-seroprotection with an adjusted odds ratio (OR) of 3.2, 9.4, and 9.9 among children aged 5-10, 11-15, and > 15 years, respectively, compared to younger children ( < 0.001). About 85% of non-seroprotected children developed an anamnestic response after receiving the booster dose, and 84.3% of responders had a good response ( 100 IU/L). Undetectable pre-booster titer was found to be the only risk factor for non-response to booster with OR = 3.2 ( < 0.010). About 95.7% of children who were not responding to booster dose developed immune response after receiving the three doses of HBV vaccine.

Conclusions: Older age of children was the only significant predictor for HBV non-seroprotection. High anamnestic response rate signifies the presence of immune memory with long-term protection despite the waning of anti-HBs over time. However, some children with pre-booster undetectable anti-HBs titers may be unable to develop anamnestic response, and a second vaccination series might be necessary for HBV protection for these children.