Changes of Anti-H. influenzae Type b IgG in the Sera of Korean Infants and Children after Birth

ABSTRACT

PURPOSE: Most of invasive Haemophilus influenzae diseases occur in children under 5 years of age, and are due almost exclusively to type b strain. Although antibodies to several surface antigens of H. influenzae play a role in conferring immunity, antibody to the type b capsular polysaccharide appeared to have the most important protective functions. However, the antibody response to vaccines or natural infections are quite differ according to the ages and ethnic groups. This study was performed to investigate the need of Hib vaccination and its appropriate time in Korean infants. METHODS: Three hundred and forty-five Korean infants and children who were relatively well without history of Hib vaccination or infection were enrolled in the study. All subjects did not receive blood transfusion or blood products and also had no any immunological abnormalities. Anti-PRP IgG was measured in the sera of subjects using ELISA. PRP-albumin was used as a coating antigen. RESULTS: Geometric mean titer (GMT) of anti-PRP IgG in the sera of neonates was 0.594 g/ml and was gradually decreased to 0.186 g/ml and 0.111 g/ml at 2 and 3 months of age, respectively. Ant-PRP IgG was significantly low after 3 months of age, and was gradually increased after 10 months of age. Anti-PRP IgG level p> or = 0.15 g/ml was observed in 70.8% (17/24) in neonatal group, 41.6% (10/24) and 18.7% (3/16) in 2 and 3 months of age. Only 8.7% (10/115) showed anti-Hib IgG levels of p> or = 1.0 g/ml, which has been considered as a level of longterm protection, was observed in 37.5% (9/24) in neonates, 12.5% (3/24) in 2 months of age and less then 10% thereafter. CONCLUSIONS: These results suggest that congenital passive immunity can be obtained enough in Korean infants and was rapidly decreased during the period of 3 months after birth. Hib vaccination will be recommended at early infancy (2 months of age) to provide appropriate antibodies in Korean children.