• Clinical and Experimental Pediatrics
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• v.50 no.5
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• pp.449-456
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• 2007

Purpose : Antibody persistence after primary series of Haemophilus influenzae type b (Hib) vaccine and responses to a boosters are little known in Korean children. We performed this study to evaluate the antibody titer in relation with a booster immunization of Hib vaccine in Korean children. Methods : One hundred forty-four children aged 12-23 months old were enrolled in three university hospitals. The immunogenicity of a boosters with Hib vaccine was assessed in children previously primed with Hib vaccine. Antibody persistence was also assessed in children who had received 3 doses of Hib vaccine without a booster. Anti-polyribosylribitol phosphate (PRP) IgG antibody levels and bactericidal titers were determined by enzyme immunoassay and bactericidal assay at the Center for Vaccine Evaluation and Study, Medical Research Institute, Ewha Womans University. Results : Prior to a booster in the second year of life, geometric mean antibody concentrations were $2.39{\mu}g/mL$ and the percent of subjects who had a anti-PRP antibody level ${\geq}1{\mu}g/mL$ was 68.6%. After boosting, antibody concentration was $19.09{\mu}g/mL$ and the percent of subjects who had a anti-PRP antibody level ${\geq}1{\mu}g/mL$ was 96.5%, which reflects previous immune priming. In subjects who had finished primary immunization only, the bactericidal titer was 3,946 and in subjects who had a booster, it was 11,205. Anti-PRP antibody level was correlated with serum bactericidal titer. Conclusion : Many children aged 12-23 month old still had protective antibodies after recommended primary immunization only. A booster dose seemed to induce good anamnestic antibody responses in Korean children.