IMMUNE-RESPONSES OF INFANTS VACCINATED WITH SEROTYPE 6B PNEUMOCOCCAL POLYSACCHARIDE CONJUGATED WITH TETANUS TOXOID

Background. Streptococcus pneumoniae is a major cause of meningitis, b acteremia, pneumonia and otitis media. Pneumococcal polysaccharides ar e not immunogenic in infants, but improved immunogenicity of polysacch aride-protein conjugates has been demonstrated. Antibiotic-resistant p neumococci have increased the need for an effective vaccine. Objective . To study the safety and immunogenicity of a pneumococcal type 6B pol ysaccharide-tetanus toxoid conjugate (Pn6B-TT) in infants and to asses s the function of antibodies. Methods. Healthy infants were injected, Group A at 3, 4 and 6 months (n = 21) and Group B at 7 and 9 months (n = 19). Booster injection was given at 18 months. Antibodies were meas ured by enzyme-linked immunosorbent assay and radioimmunoassay, and fu nctional activity was measured by opsonization of radiolabeled pneumoc occi. Nasopharyngeal cultures were obtained. Results. No significant a dverse reactions were observed. Pn6B-IgG (enzyme-linked immunosorbent assay) increased to a geometric mean of 0.62 mu g/ml (P = 0.367, compa red with prevaccination titers) in Group A at 7 months and 1.22 mu g/m l (P < 0.001) in Group B at 10 months. Total Pn6B antibodies (radioimm unoassay) were 44 ng of antibody N/ml (P < 0.053) in Group A and 211 n g of antibody N/ml (P < 0.001) in Group B. A smaller increase in IgM a nd IgA anti-Pn6B was observed. Reinjection at 18 months elicited boost er responses in total and IgG anti-Pn6B; 62% of those in Group A and 7 9% of those in Group B had >300 ng of antibody N/ml. Opsonic activity, after initial and booster vaccinations, correlated with Pn6B-antibody titers. Three infants with nasopharyngeal cultures repeatedly positiv e for serogroup 6 had poor serum IgG responses. Conclusion. Our result s demonstrate that Pn6B-TT is safe, elicits functional antibodies and memory responses in infants.