Evaluation of Haemophilus influenzae Type b Vaccine for Routine Immunization in Nepali Infants

BACKGROUND: Haemophilus influenzae type b (Hib) carriage and disease studies in Nepali children suggest a significant burden of infection. Hib conjugate vaccines (HibCV) do not have uniform immunogenicity between populations. We determined the immunogenicity of HibCV in Nepali infants, before its introduction into the routine immunization schedule. METHODS: Ninety infants recruited at Patan Hospital, Kathmandu, received 3 doses of the HibCV with routine immunizations (diphtheria, tetanus, whole cell pertussis-hepatitis B vaccine + oral polio vaccine) at 6, 10 and 14 weeks of age, and a HibCV booster at 52 weeks. Anti-polyribosylribitol phosphate (PRP) concentrations were measured at 18, 52 and 56 weeks, and the antibody persistence at 52 weeks was compared with antibody values in unimmunized controls (n = 30). RESULTS: After 3 doses of primary immunizations, at 18 weeks of age (n = 74), all infants had anti-PRP concentrations above the accepted thresholds for short- and long-term protection (0.15 and 1.0 µg/mL, respectively). At 1 year of age, before administration of the booster of HibCV, the anti-PRP geometric mean antibody concentration was 2.76 µg/mL (confidence interval: 1.88-4.07) in sera from the immunized children compared with 0.11 µg/mL (95% confidence interval: 0.08-0.17) in the nonimmunized control group (n = 30). Twenty-seven percent (20/74) of participants, however, had anti-PRP concentrations