Immunogenicity and safety of four different doses of Haemophilus influenzae type b-tetanus toxoid conjugated vaccine, combined with diphtheria–tetanus–pertussis vaccine (DTP-Hib), in Indonesian infants

Widespread use of Haemophilus influenzae type b (Hib) conjugated vaccine in industrialized countries has resulted in a dramatic decline in the incidence of invasive Hib diseases, but the vaccine's cost has prevented its inclusion in basic immunization programs in developing countries. To overcome this problem, combination with diphtheria–tetanus–pertussis (DTP) vaccine or reduction in the dose of Hib vaccine has been proposed. To evaluate the immunogenicity and adverse reactions from lower doses of Hib-polyribosylphosphate (PRP) conjugated with tetanus toxoid (PRP-T), a double-blind study was conducted in Jakarta, Indonesia, and its suburbs. A total of 1048 infants 6 weeks to 6 months of age received three doses of DTP vaccine combined with the usual 10μg dose or with a reduced dose of 5, 2.5 or 1.25μg of PRP-T at two-monthly intervals. Antibodies were measured prior to the first dose and 4–6 weeks following the third dose. Adverse reactions were similar among all four groups. The only significant difference was a higher rate of irritability (p<0.02) and of temperature elevation >38°C (p<0.009) after doses 1 and 2 in the lowest dose group (1.25μg PRP-T) compared to the other groups.