Haemophilus influenzae type b carriage in Indigenous children and children attending childcare centers in the Northern Territory, Australia, spanning pre- and post-vaccine eras

The continuing role ofHaemophilus influenzaetype b carriage surveillance as a mechanism for early detection of invasive disease activity

“…25 However, despite the marked disappearance of invasive Hib disease, some studies encompassing mostly Indigenous populations report persisting Hib carriage, albeit at lower levels than pre-vaccination carriage. 2,11,21,23,50,53 The issue of persistent Hib carriage in vaccinated populations occurs globally, mostly in minority populations, often despite high levels of vaccine uptake. 2,12 A study of Native Alaskans reported Hib oropharyngeal carriage as high as 9.3% in fully vaccinated under five year old children.…”

“…This social and demographic risk, has been associated with increases Hib carriage and for this reason, these centers are often targeted for routine surveillance of Hib carriage and other childhood pathogens. 21,33,38,70,71,73,[80][81][82][83][84][85][86][87] Special efforts to immunize children attending day-care centers need to be continually emphasized as this poses a higher risk to Hib than for children who do not attend day-care.…”

“…66 Differences between Maori and Caucasian Hib disease in children from New Zealand are less marked than for Australian Aboriginals vs. non-Aboriginal children, especially in the NT. 68 More recently, Jacups et al report persisting carriage in high risk groups from in the NT of Australia, despite high rates of Hib vaccination in NT children (98.5% adequately immunized), 21,67 Hemophilus influenzae type b Hib carriage rates reported in Indigenous (Australian Aboriginal) children from remote communities were 3.4%, while children attending childcare centers in urban centers had rates of 0.2% carriage. 21 Furthermore, Indigenous children were first colonized with Hib at a younger age, median age 3.5 mo, in contrast to urban child-care center children median age was 6.9 mo, suggesting an inadequate vaccine response or waning antibody levels low enough to permit colonization.…”

“…This vaccine was chosen for use in Indigenous and non-Indigenous children as it elicits a higher immune response after the first dose and is thus efficacious at a younger age. 13,21 Difficulties with supplies have necessitated a change in vaccine schedule, to 4 doses of PRP-T (2, 4, 6, 12 mo from January 2010), this too may affect carriage and (in time) invasive disease rates. 21 However, the corollary of vaccination indicates that while conjugate vaccines best promote T-cell-dependent responses, and in-turn a higher serum anti-PRP level, they do not raise the IgA antibody concentration at the mucosal interface.…”

“…13,21 Difficulties with supplies have necessitated a change in vaccine schedule, to 4 doses of PRP-T (2, 4, 6, 12 mo from January 2010), this too may affect carriage and (in time) invasive disease rates. 21 However, the corollary of vaccination indicates that while conjugate vaccines best promote T-cell-dependent responses, and in-turn a higher serum anti-PRP level, they do not raise the IgA antibody concentration at the mucosal interface. 22 Findings on Hib carriage dynamics from the Dominican Republic, 23 report on serum anti-Hib capsular polysaccharide (CPS) levels between vaccinated and unvaccinated infants of the same age.…”