Recent studies in the United States and Europe have shown that Haemophilus influenzae type b polysaccharide-protein conjugate vaccines can induce protective antibody levels in young infants, but it was not clear that this would be the case in African infants, to whom H influenzae vaccines must be given at a very early age to prevent disease caused by H influenzae. Therefore, antibody responses to an H influenzae type b polysaccharide-Neisseria meningitidis outer membrane protein conjugate vaccine were measured in very young Gambian infants. In the first group (n = 85), to whom the vaccine was given at the ages of 1 and 3 months, the geometric mean antibody level rose from a prevaccination level of 0.23 µg/mL to a postvaccination level of 1.27 µg/mL, and in the second group (n = 56), vaccinated at the ages of 2 and 4 months, the prevaccination level of 0.16 µg/mL rose to a postvaccination level of 1.59 µg/mL. These two final postvaccination levels did not differ significantly, and interpolation suggests that similar antibody levels were present in both groups of infants at the age of 3 months. This is the age by which protection would need to be achieved to protect against H influenzae meningitis in The Gambia and in other countries where the infection has similar epidemiologic characteristics. No significant side effects of vaccination were noted.
