Abstract 57 Poster Session III, Monday, 5/3 (poster 171)

Pneumococcal infections are an important cause of mortality and morbidity in children with sickle cell disease (SCD), especially those under 2 years of age. Pneumococcal conjugate vaccines linked to protein carriers are immunogenic in healthy infants, but have not been evaluated in children with SCD. Infants with SCD were immunized with a 7-valent pneumococcal polysaccharide-protein conjugate vaccine (Wyeth- Lederle Vaccines & Pediatrics) at 2, 4, and 6 months. A booster dose of 23-valent polysaccharide pneumococcal vaccine (Pnu-Immune®) was administered at 24 months. Anti-Streptococcus pneumoniae type 6B and 14 IgG antibodies were measured by ELISA after preabsorption with C-polysaccharide. Serum opsonic activity was measured in order to assess the biologic function of the antibody. The opsonic assay used radiolabelled killed bacteria, patients' heat-inactivated serum (to eliminate the effect of complement) and peripheral blood PMNs. An opsonic index was calculated with the formula: (PMN-associated bacteria cpm / total bacterial input cpm) × 100%. (Table)

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Conclusions: This pneumococcal conjugate vaccine is immunogenic in infants with SCD and induces complement-independent serum opsonic activity. Levels of both antibody and opsonic activity for both serotypes increase significantly after a booster dose of polysaccharide vaccine at 24 months. Serum opsonic activity correlates with antibody levels.

(Supported by Wyeth-Lederle Vaccines & Pediatrics, Thrasher Fund, and Thomas Wilson Sanitarium)