Experience with the prevention of invasive Haemophilus influenzae type b disease by vaccination in Alaska: The impact of persistent oropharyngeal carriage

Objectives: To report the epidemiology of invasive Haemophilus influenzae t ype b (Hib) disease in high-risk Alaska Native infants before and after uni versal infant Hib vaccination and evaluate an increase in invasive Hib dise ase in 1996 after changing Hib vaccine type. Study design: Statewide laboratory surveillance for invasive Hib disease ha s been conducted since 1980. Three cross-sectional Hib carriage studies wer e conducted in 1997 and 1998. Results: The invasive Hib disease rate in Alaska Natives decreased from 332 cases per 100,000 children <5 years old in 1980-1991 to 17:100,000 in 1992 -1995 but increased primarily in rural areas to 57.9:100,000 after a switch in Hib vaccine types; Carriage studies in 5 rural Alaska Native villages s howed oropharyngeal Hib carriage as high as 9.3% in children aged 1 to 5 ye ars; in contrast, carriage in urban Alaska Native children was <1%. Conclusions: Although Hib disease has decreased in Alaska, the rate of Hib disease and carriage in rural Alaska Natives did not decrease to the same e xtent as in non-Natives and urban Alaska Natives. Use of polyribosylribitol phosphate-outer-membrane protein conjugate vaccine for the first vaccine d ose is critical to disease control in this population with continued transm ission in infants <6 months of age. The ability to eliminate Hib carriage a nd disease may be affected by population characteristics, vaccination cover age, and Hib vaccine type used. This may pose a challenge to global elimina tion of Hib.