Eradication of Haemophilus influenzae Type b Disease in Southern California

Objective: To assess the effects of Haemophilus influenzae vaccination of infants. Research Design: We evaluated H influenzae type b (Hib) disease rates in Los Angeles County, California (population, 9 million; 1983 through 1992), and in the Southern California Kaiser Health Plan (2.5 million enrollees; 1988 through 1992) during the past decade. Cases were obtained through active and passive disease surveillance in the two populations. The following vaccines were used during the study period (1983 through 1992): (1) Hib polysaccharide vaccine (polyribosyl ribitol phosphate) (used from 1985 through 1987 for children 24 through 60 months of age); (2) Hib polysaccharide-diphtheriatoxoid conjugate, Hib polysaccharide CRM₁₉₇ mutant diphtheria toxoid conjugate vaccine, and Hib polysaccharide outer-membrane protein of group B meningococcus conjugate vaccine in older children (1988 through 1990; ages 15 through 60 months); and (3) Hib polysaccharide CRM₁₉₇ mutant diphtheria toxoidconjugate vaccine and Hib polysaccharide outer-membrane protein of group B meningococcus conjugate vaccine used in infants (1991 through 1992). Measurements and Results: Between 1983 and 1988, the Hib disease incidence in Los Angeles County was unchanged (32.7 to 42.5/100 000 person-years in children younger than 5 years). In 1989 through 1990, before Hib conjugate licensure for infant use, Hib disease rates in all age groups declined. After licensure of Hib vaccines for infants in 1990, there was a further fivefold decrease in infants. More dramatic decreases occurred in the better-immunized Kaiser Health Plan children aged 0 through 60 months (53 cases in 1989, only two cases in 1992). Conclusions: The Hib disease has been nearly eradicated in a fully immunized population (Kaiser Health Plan), and significant reductions have also occurred in Los Angeles County.