Haemophilus influenzae Type b Conjugate Vaccines: Update

Abstract

The purpose of this statement is to update previous information and recommendations provided by the Committee for the use of Haemophilus influenzae type b conjugate vaccines in view of the licensure of a new product. Our initial recommendations concerned the use of PRP-D, a vaccine consisting of the capsular polysacchanide of H influenzae type b conjugated to diphtheria toxoid, which was licensed for use in December 1987. On December 22, 1988, a second conjugate vaccine was licensed by the US Food and Drug Administration for the prevention of infections caused by H influenzae type b in children 18 months of age or olden. This newly licensed vaccine is a conjugate of H influenzae type b capsular oligosaccharide and a nontoxic mutant diphtheria toxin protein molecule called CRM197. The official designation of this vaccine is "Haemophilus b conjugate vaccine (diphtheria CRM197 protein conjugate)" and it is often referred to as HbOC. No serious adverse reactions have been reported in clinical trials to date. Among 265 infants in the United States between 16 and 23 months of age who received HbOC, 7.2% had temperatures exceeding 38°C, 1.5% had erythema and warmth at the injection site, and 0.8% had localized swelling. Like PRP-D, HbOC is more immunogenic in 18-month-old children than are the unconjugated polysacchanide vaccines (PRP). Among 212 HbOC recipients in the study, the geometric mean anticapsular antibody concentration 1 month after immunization was 13.11 µg/mL. Moreover, 98.1% of these infants had an antibody concentration in excess of 1µg/mL, a concentration associated with protection in a Finnish field trial of unconjugated PRP.