HAEMOPHILUS INFLUENZAE TYPE B (Hib) CAPSULAR ANTIGEN (PRP) CONJUGATE VACCINE INDUCES ANTI-PRP ANTIBODY (Ab) IN CHILDREN FOLLOWING Hib INFECTIONS

Abstract

PRP vaccine is a poor immunogen when administered to some children following Hib infection or their sibs. To date, we have immunized 18 patients (mean age 19 mos., range 7-45 mos; 14 meningitis) with PRP-diphtheria toxoid conjugate vaccine (PRP-D) containing 20 μg PRP. Children were inoculated 1-8 mos. (15 ≤ 2 mos.) post illness with 1 or 2 doses of PRP-D. Serum was obtained for anti-PRP Ab (radioantigen binding assay at Connaught Laboratories) prior to and 1 month post vaccine. Serology is available on 13 patients, 6 of whom were Ab negative ( < 0.012 μg/ml) pre-vac (4 were ≤ 16 mos. when immunized). Anti-PRP rises developed in 11/13 patients and 5/6 pre-vac Ab negative patients. The pre- and post-geometric mean titers were 0.13 and 2.0 μg/ml, respectively (p < 0.001 for log transformed data). One patient (pre-vac Ab neg), a non-responder to routine PRP given at 24 mos., developed 0.28 ug/ml anti-PRP Ab following PRP-D at 26 mos. Anti-PRP Ab developed in 3/3 sibs, (8, 11, and 24 mos.), 2 of whom were Ab negative pre-vac. Our data indicate that young children who may not have developed anti-PRP within 1 or 2 mos. of Hib infection usually respond to 1 or more doses of PRP-D and suggest that children at increased risk for Hib disease will likely respond to PRP conjugate vaccines.