EVALUATION OF THE NEED TO IMMUNIZE CHILDREN WITH SICKLE CELL DISEASE WITH HEMOPHILUS INFLUENZAE TYPE B (HIB) VACCINE

Abstract

Insufficient data are available in which to base recommendations for the use of HIB polysaccharide vaccine in children older than 18-24 months who have functional asplenia who may be at increased risk for HIB systemic disease. Therefore, using a radioimmunoassay for detection of antibodies to the capsular polysaccharide of HIB, polyribosylribitolphosphate (PRP), we determined the PRP specific antibody levels in 36 children, age 2-20 years (mean 8.9 years) with SS or SC disease cared for in our hematology clinic to assess their potential risk for acquiring HIB disease. Although a precise protective level of PRP antibody has not been established with certainty, we used a level of 1 ug/ml to determine risk based on results generated in the Finnish field trial correlating this level with short term clinical protection. 20/36 (56%) of the children evaluated had PRP antibody levels less than 1 ug/ml. 15 of these “at risk” children (75%) were ≥ 5 years of age, with 8 children being 10 years of age or older. In fact, 10/20 (50%) “at risk” children had PRP antibody levels < 0.25 ug/ml with 50% of these being older than 5 years of age. Based on these data showing low levels of PRP antibody in older children with hemoglobinopathies, recommendations for administration of HIB vaccine should be extended to all children with such chronic conditions.