Background: The emergence of resistant pneumococci makes the treatment of pneumococcal diseases difficult. The currently available polysaccharide vaccines have very limited efficacy in young children. The immunogenicity can be improved by covalent coupling to protein carriers as has been shown with Haemophilus influenzae type b.
Methods: Thirty healthy infants were immunized with a pneumococcal conjugate vaccine at 2, 4 and 6 months of age. Oligosaccharides were derived from capsular polysaccharides of types 6B, 14, 18C, 19F and 23F and conjugated to the nontoxic mutant diphtheria toxin CRM197. The final vaccine was a mixture of these conjugates, containing 10 micrograms of each oligosaccharide. The infants received simultaneously H. influenzae type b oligosaccharide-CRM197 conjugate vaccine. Serum samples were taken before each dose and 1 month after the third dose. Control material was composed of 25 serum samples taken from children of the same age without pneumococcal vaccination. Enzyme-linked immunosorbent assay was used to measure serum IgG anti-pneumococcal polysaccharide concentrations and radioimmunoassay for the serum Ig anti-H. influenzae type b concentrations.
Results: PncCRM vaccine was well-tolerated. Pneumococcal type 18C induced a significant antibody increase after the first dose, whereas the other five oligosaccharides, including H. influenzae type b oligosaccharides, induced an increase after the second or third dose. The specific IgG concentrations at 7 months of age were significantly higher among the vaccinated infants than in the controls for all the five pneumococcal types.
Conclusions: Pneumococcal oligosaccharide-CRM197 conjugate vaccine is able to induce an IgG serum response in infants and anti-pneumococcal antibody concentrations were significantly higher than in controls of same age.