Immune responses of infants vaccinated with serotype 6B pneumococcal polysaccharide conjugated with tetanus toxoid.
BACKGROUND
Streptococcus pneumoniae is a major cause of meningitis, bacteremia, pneumonia and otitis media. Pneumococcal polysaccharides are not immunogenic in infants, but improved immunogenicity of polysaccharide-protein conjugates has been demonstrated. Antibiotic-resistant pneumococci have increased the need for an effective vaccine.


OBJECTIVE
To study the safety and immunogenicity of a pneumococcal type 6B polysaccharidetetanus toxoid conjugate (Pn6B-TT) in infants and to assess 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 measured by enzyme-linked immunosorbent assay and radioimmunoassay, and functional activity was measured by opsonization of radiolabeled pneumococci. Nasopharyngeal cultures were obtained.


RESULTS
No significant adverse reactions were observed. Pn6B-IgG (enzyme-linked immunosorbent assay) increased to a geometric mean of 0.62 microgram/ml (P = 0.367, compared with prevaccination titers) in Group A at 7 months and 1.22 micrograms/ml (P < 0.001) in Group B at 10 months. Total Pn6B antibodies (radioimmunoassay) were 44 ng of antibody N/ml (P < 0.053) in Group A and 211 ng of antibody N/ml (P < 0.001) in Group B. A smaller increase in IgM and IgA anti-Pn6B was observed. Reinjection at 18 months elicited booster responses in total and IgG anti-Pn6B; 62% of those in Group A and 79% 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 positive for serogroup 6 had poor serum IgG responses.


CONCLUSIONS
Our results demonstrate that Pn6B-TT is safe, elicits functional antibodies and memory responses in infants.
Sigurdardottir
S T
ST
Department of Immunology, National University Hospital, Reykjavik, Iceland.
Vidarsson
G
G
Gudnason
T
T
Kjartansson
S
S
Kristinsson
K G
KG
Jonsson
S
S
Valdimarsson
H
H
Schiffman
G
G
Schneerson
R
R
Jonsdottir
I
I
D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology; D005260:Female; D006801:Humans; D007071:Immunoglobulin A, Secretory / Q000032:analysis; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000382:microbiology; D010587:Phagocytosis; D011135:Polysaccharides, Bacterial / Q000009:adverse effects / Q000276:immunology*; D012463:Saliva / Q000276:immunology; D013296:Streptococcus pneumoniae / Q000302:isolation & purification; D013745:Tetanus Toxoid / Q000009:adverse effects / Q000276:immunology*; D014611:Vaccination; D018074:Vaccines, Conjugate / Q000276:immunology
D000907:Antibodies, Bacterial; D007071:Immunoglobulin A, Secretory; D011135:Polysaccharides, Bacterial; D013745:Tetanus Toxoid; D018074:Vaccines, Conjugate; C092872:streptococcal polysaccharide-tetanus toxoid conjugate vaccine