Prospective comparison of the immune response of infants to three Haemophilus influenzae type b vaccines

Abstract

The antibody response to three Haemophilus influenzae type b vaccines was examined in 134 infants 17 to 22 months of age. Sera were collected from each subject before and 1 month after vaccination with either purified H. influenzae type b capsular polysaccharide (polyribosyl-ribitol phosphate (PRP] or one of two protein-conjugated vaccines (PRP-D or HbOC). Comparison of the two conjugate vaccines revealed that HbOC produced an antibody response greater than or equal to 1.0 micrograms/ml in 96% compared with 72% who were vaccinated with PRP-D (P less than 0.05). The isotype distribution of the antibodies produced by the two vaccines was similar. While all of the vaccines resulted in higher concentrations of anticapsular IgG1 than IgG2, the IgG1:IgG2 ratio was significantly higher in subjects immunized with HbOC. The IgG1:IgG2 ratio was similar in subjects immunized with PRP or PRP-D. The clinical significance of these observations remains to be determined.