Immunogenicity of Haemophilus influenzae PRP-D Conjugate Vaccine in Korean Infants

ABSTRACT

PURPOSE: Infection by Haemophilus influenzae Type B(Hib) occurs most often in infants and children who are 5 years old and less. The incidence is highest around 6 months of age, and then decreases thereafter as infants gain natural immunity. Hi PRP-D conjugate vaccine is poorly immunogenic in infants. However, immunogenicity PRP-D vaccine in Korean infants is unknown. This study was carried out to evaluate the immunogenicity of PRP-D in Korean infants. METHODS: Forty-two normal infants who were born in Hanil General Hospital from February 1994 to July 1995 were vaccinated at 2, 4, 6, 15 months after birth. The serum antibody level was measured at 2, 6, 7, 15, 16 months of age. The infants also received DTaP, TOPV at 2, 4, 6 months and MMR at 15 months. Anti-PRP antibody level was measured by radioimmnune assay at Dana Faber Cancer Institute in Boston, U.S.A. RESULTS: The geometric mean of Anti-PRP antibody titers were 0.074microgram/ml at 2 months, 0.185 microgram/ml at 6 months, 1.390microgram/ml at 7 months, and then fell to 0.501microgram/ml at 15 months(Mean values are geometric mean; L=512, P=0.0001). Anti-PRP antibody titers increased in proportion to the number of vaccinations. The proportion of infants with anti-PRP antibody titers> OR =0.15microgram/ml were 15.8% at 2 months, 44.7% at 6 months, and 94.7% at 7 months. The proportion of infants with anti-PRP antibody titers> OR =1.0microgram/ml were 2.6% at 2 months, 26.3% at 6 months, and 57.9% at 7 months(X2 test; total X2=27.64, P<0.01; male X2=23.05, P<0.01; female X2=48.55, P<0.01). CONCLUSION: The immunogenicity of PRP-D conjugate vaccine may be more effective in young Korean infants than in other population published in studies. The clinical implication of good responsiveness of Korean infants to PRP-D vaccine needs further evaluations.