Comparison of pneumococcal vaccination response in children with sickle cell disease: HbSS and HbSC

Abstract

Introduction: Sickle cell disease (SCD) children are at increased risk of invasive pneumococcal disease and rely on penicillin prophylaxis and vaccination for infection prevention. Post-vaccination antibody levels in SCD may wane overtime. HbSC are believed to have better immunological response than HbSS.

Objective: To compare antibody response to 23-valent pneumococcal polysaccharide vaccine (PPSV-23) between HbSS and HbSC.

Methods: Patients with HbSS (n=33) and HbSC (n=11), aged 7-18 years, were prospectively recruited. Luminex pneumococcal antibody levels were measured for 23-serotypes, after two PPSV-23 doses.

Results: Absolute median titer for 20 of the 23 serotypes was higher in HbSC than HbSS and significantly higher for serotypes 22 (3.9 vs. 1.6mcg/ml; p=0.039) and 43 (2.9 vs. 0.8mcg/ml; p=0.007). HbSC mounted a better immune anti-pneumococcal response compared to HbSS (≥1.3mcg/ml) for 18 of 23 serotypes, albeit not significant for any of the serotypes. More HbSC (64%) than HbSS (42%) were good vaccine responders (p=0.303). Two of 21 (10%) good vaccine responders and nine of 23 (39%) poor vaccine responders SCD participants subsequently developed acute chest syndrome or pneumonia (p=0.036). None of the HbSC patients developed ACS after receiving PPSV-23. HbSS poor vaccine responders were at increased future recurrence risk for ACS (p=0.003), pneumonia (p=0.036) or both (p=0.011), compared to good vaccine responders.

Conclusion: HbSC possess better pneumococcal vaccine response than HbSS. Poor vaccine response is concerning for future acute pulmonary events. Current vaccination strategy for SCD sub-types are lacking, therefore further study to evaluate utility of vaccine boosters is necessary.

Keywords: HbSC; HbSS; Immunity; Pneumococcus; Sickle cell disease; Vaccine.