Objectives: This report describes the epidemiology of Haemophilus influenzae type b (Hib) invasive disease and oropharyngeal colonization among Navajo and White Mountain Apache children younger than 7 years in an era of widespread immunization.
Methods: We conducted active surveillance for invasive H influenzae disease from 1992 to 1999 and an oropharyngeal carriage study from 1997 to 1999. The predominant vaccine used was PedvaxHib.
Results: The average annual incidence of invasive Hib disease among children younger than 24 months was 22 cases per 100,000. Of 381 children younger than 7 years, only 1 (0.3%; 95% confidence interval = 0.0%, 1.3%) was colonized with Hib; 370 (97%) had received 2 or more doses of Hib conjugate vaccine.
Conclusions: Among Navajo and White Mountain Apache children, Hib conjugate vaccines have led to a sustained reduction in invasive Hib disease and a reduction in oropharyngeal Hib carriage. The disease incidence among children younger than 24 months remains 20 times higher than in the general US population. Hib elimination will require additional characterization of colonization and disease in these high-risk populations.