Immunogenicity and reactogenicity of Haemophilus influenzae type b-meningococcus group B outer membrane protein conjugate vaccine in children 2-60 months of age.

Haemophilus influenzae b - Neisseria meningitidis group B outer membrane protein conjugate vaccine (Hib-OMP) was given to 571 children 2-60 months of age. Two doses of Hib-OMP were given, 2 months apart, to 2-11 month old infants, and a single dose to children 12-60 month old. Sera were obtained from a subset of vaccinees at each immunization, and at follow-up 1 month and 1 year after immunization. Geometric mean antibody concentration (micrograms/ml) before and after full immunization were respectively 0.111 and 3.549 for 2-3 month old, 0.108 and 5.048 for 4-5 month old, 0.082 and 6.933 for 6-11 month old; they were 0.103 and 3.500 for 12-17 month old, 0.167 and 7.791 for 18-23 month old and 0.243 and 12.781 for children greater than or equal to 24 months. Detectable antibody (greater than or equal to 0.125 micrograms/ml) failed to develop in 2/399 (0.5%) after primary immunization, and 12/252 (4.8%) lost detectable antibody 1 year later. Six of these 12 infants were less than 12 month old. The vaccine was immunogenic as early as 3-5 months of age. The need for booster immunization needs to be assessed.