Predictors of Pneumococcal Conjugate Vaccine Immunogenicity among Infants and Toddlers in an American Indian PnCRM7 Efficacy Trial.

BACKGROUND:Pneumococcal conjugate vaccines are important for the prevention of serious illness and death among infants. Factors associated with pneumococcal conjugate vaccine immunogenicity have not been explored. METHODS:Children <24 months of age received 2, 3, or 4 doses of 7-valent pneumococcal conjugate vaccine (PnCRM7) or control vaccine depending on age at enrollment. Serum samples were tested for serotype-specific antibodies by enzyme-linked immunosorbant assay. Multiple linear regression was used to determine predictors of immunogenicity. RESULTS:Among 315 PnCRM7-vaccinated subjects and 295 control subjects enrolled at <7 months of age, geometric mean concentrations (GMCs) of antibodies were significantly higher after dose 3 than after dose 2 for all serotypes except type 4. The proportion of subjects with antibody concentrations > or =5.0 micro g/mL was higher for all serotypes, but the proportion with concentrations > or =0.35 micro g/mL was higher only for types 6B and 23F. Three-dose and 2-dose regimens for those 7-11 and 12-23 months of age, respectively, were highly immunogenic. Increased maternal antibody concentrations were associated with reduced responses to dose 1 and 3 but not to dose 4 of PnCRM7. CONCLUSIONS:Maternal antibody is associated with a reduced infant response to PnCRM7 but does not interfere with immune memory. In infants, a third priming dose increases the antibody GMC and the proportion achieving an antibody concentration > or =5.0 micro g/mL but has little impact on the proportion achieving a concentration > or =0.35 micro g/mL.