Immune responses to hepatitis B immunization 10-18 years after primary vaccination: a population-based cohort study.

We evaluated the immune response to neonatal HBV immunization in children of infected parents 10-18 years after primary vaccination. Healthy individuals immunized with an infantile course of three doses of HBV vaccine were tested for persistence of anti-HB surface antibody (HBsAb). Those with an HBsAb level of <10 IU/mL received a booster dose of the vaccine with subsequent doses to those without protective titres. HBsAb concentrations were determined 4 weeks after each dose of the booster vaccine. The data were analysed separately for three age groups: 10-11, 12-14 and 15-18 years old. A total of 541 healthy individuals were studied. The highest seroprotection rate of 48% was observed in the youngest vaccinees (10-11 years old). This declined to 26.5% in the oldest (15-18 years old) group (P = 0.008). The youngest vaccinees showed the highest rate of anamnestic immune responses (96%). However, 25% of oldest individuals failed to mount an anamnestic immune response in challenge with a booster dose of the vaccine (P = 0.005), suggesting waning immunity with increasing age. Age (OR: 0.80; P = 0.01) and prebooster HBsAb levels (OR: 0.37; P = 0.01) identified responders to first booster doses of the vaccine by logistic regression analysis. The majority of high-risk vaccinees showed anamnestic immune response 10-11 years after primary immunization. However, we found a significant proportion (25%) of older individuals with no anamnetic response, which suggests a waning of immune memory. Detailed long-term follow-up studies are necessary to determine the risk of natural infection among these individuals before a booster schedule can be recommended.