Haemophilus influenzae type b immunization of children with sickle cell diseases.

Haemophilus influenzae type B vaccine is recommended for children 1.5 to 6 years of age with sickle cell anemia, but the adequacy of their response is unknown. A total of 69 children with sickle cell syndromes, 1.5 to 5.6 years of age, were immunized with two vaccines alternatively, single blind. PRP vaccine was given to 36 children and a diphtheria toxoid conjugated vaccine, PRP-D, was given to 36. Coded pre- and postvaccine sera were tested by radioimmunoassay for anti-PRP antibody. The groups did not differ in age distribution or type of sickle hemoglobinopathy. Preexisting antibody levels were low in both vaccine groups; 65% were less than 0.15 microgram/mL. The vaccines were safe but associated with frequent minor reactions. PRP-D gave higher geometric mean titers and mean fold titer increase than PRP in all children (15.58 micrograms/mL [234-fold] v 2.63 micrograms/mL [29-fold]) and in the subgroups 1.5 to 2.5 years of age or with pretiter values less than 0.15 microgram/mL. Titers for 64% of children receiving PRP and 94% receiving PRP-D were greater than or equal to 1.0 microgram/mL. Thus, both vaccines were useful in this population, but PRP-D was more immunogenic. Duration of antibody levels postvaccination, booster responses, and PRP-D immunogenicity in younger children with sickle cell syndromes all require further study.