Safety, immunogenicity, and efficacy in infancy of oligosaccharide conjugate Haemophilus influenzae type b vaccine in a United States population: possible implications for optimal use.

Between February 1988 and June 1990, the safety, immunogenicity, and efficacy of Haemophilus influenzae type b (Hib) oligosaccharide conjugate (HbOC) vaccine was evaluated in a prelicensure trial of 61,080 children. HbOC was found to be safe and immunogenic in infancy. Extended follow-up revealed that as of 31 December 1990, 30 cases of invasive Hib disease had occurred in 74,699 children; 26 were in unvaccinated children and 4 in children who had received only one dose. No disease occurred in children who had received two or three doses. By 30 September 1991, another case had occurred in an unvaccinated child. Comparison of these efficacy data with those of Hib capsular polysaccharide-outer membrane protein conjugate vaccine (PRP-OMP) reveals that both were effective in preventing disease in the first year of life. However, the small cohort in the PRP-OMP study did not allow demonstration of duration of protection beyond 1 year. Ongoing surveillance in larger populations is necessary to allow comparison of the duration of immunity provided by these vaccines.