Immunization with oligosaccharide conjugate Haemophilus influenzae type b (HbOC) vaccine on a large health maintenance organization population : extended follow-up and impact on Haemophilus influenzae disease epidemiology

Between February, 1988, and June, 1990, the safety, immunogenicity and efficacy of the HbOC (oligosaccharide conjugate Haemophilus influenza type b) vaccine was evaluated in a prelicensure trial performed in a study population of 61,080 children within the Northern California Kaiser Permanente Medical Care Program. In this evaluation the HbOC vaccine was found to be safe, immunogenic and efficacious in infancy. Since licensure an estimated 162,000 additional doses of HbOC vaccine have been given to 75,000 additional children. In addition to reporting on extended follow-up of this population, this publication reports on the impact of immunizing a high proportion of the Northern California Kaiser Permanente Medical Care Program population in infancy and early childhood on the epidemiology of invasive disease caused by H. influenzae type b (Hib) and invasive disease caused by non-type b H. influenzae. As of January 31, 1992, six cases of Hib invasive disease have been identified in vaccinated children. Of these five occurred in children who had received only one dose of vaccine in infancy. One case of Hib meningitis occurred in a 3 1/2-year-old child who received doses of HbOC at 2, 4 and 6 months of age but no further doses of any Hib vaccines. During 1991 a total of three cases of invasive disease caused by Hib were observed in children younger than 18 months of age within the Northern California Kaiser Permanente Medical Care Program. This represents a 94% reduction in disease incidence in this age group from that observed in the years 1984 to 1987. No change in the incidence of invasive disease caused by non-type b and nontypable H. influenzae organisms has been observed since the introduction of infant vaccination.