Abstract
The currently available 7-valent pneumococcal conjugate vaccine (PCV7) elicits good immune response to and is effective against vaccine serotypes. However, its effectiveness against vaccine-related serotypes is variable. Serum samples were obtained 1 month after the last vaccination from 31 infants immunized with PCV7 at 2, 4, and 6 months of age. The sera were used to determine immunoglobulin G antibody levels to eight serotypes (seven vaccine serotypes and serotype 19A) with enzyme-linked immunosorbent assay (ELISA) and opsonic capacity against 11 serotypes (seven vaccine serotypes, serotypes 19A and 6A, and nonvaccine serotypes 5 and 7F) using a multiplexed opsonization assay. ELISA results showed antibody concentrations varied between 1.84 and 10.49 microg/ml, and all subjects had antibody concentrations of >or=0.35 microg/ml for all serotypes, including serotype 19A. In contrast, the opsonic index was detectable (i.e., opsonic index >or= 8) in all children for the seven vaccine serotypes, 81% for serotype 6A, and merely 19% for serotype 19A. PCV7 shows good immunogenicity for vaccine serotypes in infants after a primary series. PCV7 does not elicit opsonic antibodies to serotype 19A. ELISA may thus be an inadequate surrogate assay for evaluating the response for cross-reactive serotypes in infants.
Highlights
The currently available 7-valent pneumococcal conjugate vaccine (PCV7) elicits good immune response to and is effective against vaccine serotypes
The children in the present study produced good immune responses in vaccine serotypes (VTs) after a primary series of PCV7 when the responses were estimated by either opsonization assay (OPA) or enzyme-linked immunosorbent assay (ELISA)
PCV7 elicits strong protective immunity against the seven VTs in the children in this study as determined by both assay methods, and our study confirms usefulness of ELISA in estimating the immune protection induced for VT with PCV7
Summary
The currently available 7-valent pneumococcal conjugate vaccine (PCV7) elicits good immune response to and is effective against vaccine serotypes. Reverse cumulative distribution curves were used to display the percentages of children that achieved different antibody concentrations to each of the seven vaccine type pneumococcal serotypes and VRTs 19A and 6A.
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