K. Galil et al., Reemergence of invasive Haemophilus influenzae type b disease in a well-vaccinated population in remote Alaska, J INFEC DIS, 179(1), 1999, pp. 101-106
Before vaccination, Alaska Natives experienced very high rates of invasive
Haemophilus influenzae type b (Hib) disease and carriage. Vaccination with
Hib conjugate vaccine PRP-OMP (polyribosylribitol phosphate Neisseria menin
gitidis outer membrane protein) began in 1991 and resulted in a sharp decli
ne in cases. In 1996, after switching to a different Hib conjugate vaccine,
DTP-HbOC (which combines diphtheria-tetanus-whole cell pertussis vaccines
with HbOC [Hib oligosaccharide CRM197]), cases of invasive Hib disease incr
eased, suggesting ongoing Hib transmission despite widespread vaccination.
To determine the prevalence of and risk factors for carriage, a cross-secti
onal study of oropharyngeal Hib carriage was conducted among Alaska Native
children aged 1-5 years in remote southwestern Alaska. Of 496 children with
swabs taken, 46 (9.3%) were colonized with Hib, Carriage rates varied by v
illage from 2.2% to 13.2% and by age from 6.1% in 1-year-olds to 14.7% in 5
-year-olds. Crowding was associated with Hib carriage. Widespread vaccinati
on with PRP-OMP Hib conjugate-vaccine did not eliminate carriage in this po
pulation of Alaska Natives, and ongoing carriage contributed to disease res
urgence.