Comparison of an opsonophagocytic assay and IgG ELISA to assess responses to pneumococcal polysaccharide and pneumococcal conjugate vaccines in children and young adults with sickle cell disease

Children with sickle cell disease were immunized with either 2 doses of 7-v alent pneumococcal conjugate vaccine followed by 1 dose of 23-valent pneumo coccal polysaccharide vaccine or a single dose of 23-valent vaccine. Functi onal antibodies to 7 vaccine serotypes were measured by a flow cytometric o psonophagocytic assay (OPA) and compared with IgG anticapsular polysacchari de antibody concentrations measured by ELISA, Moderate correlations were fo und between OPA and ELISA antibody titers for all 7 serotypes (r values, 0. 41-0.70; P<.001 for all serotypes). After immunization with 23-valent vacci ne, geometric mean antibody titers by OPA were significantly higher in the combined schedule group for 5 of 7 vaccine serotypes but were significantly higher for only 2 of 7 serotypes as measured by ELISA, The ability of OPA to show a greater differential response to the 2 immunization schedules use d in this study suggests that it may be useful in the evaluation of immuniz ation regimens involving pneumococcal conjugate vaccines.