Haemophilus influenzae is a Gram-negative coccobacillus. Serotype b of Hib is a leading cause of serious disease, particularly in childhood. It can cause diseases of the respiratory tract including otitis media, sinusitis and bronchitis. Serious manifestations of Hib disease include meningitis, bacteraemia, epiglottitis, septic arthritis, pericarditis, osteomyelitis, soft tissue abscesses and cellulitis, and death. Other diseases, such as epididymitis, endocarditis, peritonitis and tracheitis, have also been associated with Hib.3

Relevant vaccine history

1993

  • Hib vaccine recommended in childhood vaccination schedule for all children. PRP-OMP*-containing vaccines, providing protection at an earlier age than other vaccines, used for Aboriginal and Torres Strait Islander children.

2005

  • PRP-OMP* used in the Northern Territory, Queensland, South Australia and Western Australia for Indigenous children.
  • Combined DTPa-hepB-IPV-Hib (PRP-T) or PRP-OMP* used for non-Indigenous children in these states and all children in other jurisdictions.

2009

  • Combined DTPa-hepB-IPV-Hib (PRP-T) vaccine at 2, 4, 6 and 12 months of age used in all jurisdictions.

Key points

Rates of Hib disease are now much lower than in the pre-vaccine era, for both Aboriginal and Torres Strait Islander and other children. However, throughout the post-vaccine period, higher rates have been noted in Aboriginal and Torres Strait Islander children than in other children, with the disparity increasing over time. Notification rates are now almost 13 times higher in Aboriginal and Torres Strait Islander people than in other people. Persisting Hib carriage in Aboriginal and Torres Strait Islander people highlights the need for ongoing vigilance.

* PRP-OMP: Haemophilus influenzae type b polysaccharide conjugated to the outer membrane protein of Neisseria meningitidis

† PRP-T: Haemophilus influenzae type b polysaccharide conjugated to tetanus toxoid

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Disease trends

Enhanced Hib disease notification data for all jurisdictions for the period 1993–2010 has been presented here for those <15 years of age, the age group in whom the disease burden is primarily seen (Figure 2.1.1). When compared to the disease rates prior to 1993, notification rates in the post-Hib vaccine era were significantly lower but, between 2007 and 2010, rates among Aboriginal and Torres Strait Islander children remained higher than in other children, in whom rates remained low and stable.

Figure 2.1.1: Hib notification rates and 95% confidence intervals, all Australian states, 1993 to 2010,* <15 years of age, by Indigenous status

Figure 2.1.1: is a line chart showing  Hib notification rates and 95% confidence intervals, all Australian states, 1993 to 2010. A link to a text description follows.

* Notifications where the date of diagnosis was between 1 January 1993 and 31 December 2010.

Text description of Figure 2.1.1 (TXT 1 KB)

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Notification data are presented for all jurisdictions for the period 2007–2010. No hospitalisation data are presented for invasive Hib disease because no type-specific ICD-10 code exists.

A total of 85 notifications of invasive Hib disease were recorded during this reporting period, of which 25 (29.4%) were reported in Aboriginal and Torres Strait Islander people. The notification rate was higher in Aboriginal and Torres Strait Islander people across all age groups, with the highest rate of 5.6 per 100,000 in the 0–4 years age group (Table 2.1.1).

The highest notification rate ratio (15.7:1) was also seen in the youngest age group, followed closely by the 25–49 years and 15–24 years age groups (Table 2.1.1). The overall Indigenous to non-Indigenous rate ratio increased from 8.8:1 in the previous reporting period (2003–2006) to 12.9:1 in 2007–2010.

The ICD-10-AM/ICD-10 code G00.0 (Haemophilus meningitis) was used as the code most likely to include deaths due to Haemophilus influenzae type b. There were no deaths reported from the five reporting jurisdictions (New South Wales, the Northern Territory, Queensland, South Australia and Western Australia) for the period 2006–2010 with Haemophilus meningitis as either the underlying or a contributing cause.

Table 2.1.1: Haemophilus influenzae b notifications, all Australian states, 2007 to 2010, by age group and Indigenous status
Age group
(years)
Indigenous status Notifications* (2007–2010)
n Rate Rate ratio

* Notifications where the date of diagnosis was between 1 January 2007 and 31 December 2010.

† Average annual age-specific rate per 100,000 population.

‡ Includes cases with age unknown. Rates for all ages combined are age-standardised to the Australian Bureau of Statistics Australian population estimates for 2006.

§ Indicates statistically significant, 95% confidence intervals do not overlap 1.0.

0–4
Indigenous
15
5.6
15.7§
Other
19
0.4
5–14
Indigenous
2
0.4
8.1
Other
5
0.0
15–24
Indigenous
2
0.5
13.4§
Other
4
0.0
25–49
Indigenous
4
0.6
14.7§
Other
12
0.0
>50
Indigenous
2
0.7
9.9§
Other
20
0.1
All ages
Indigenous
25
0.9
12.9§
Other
60
0.1

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Comment

Hib notification rates have decreased significantly since the introduction of vaccines in 1993. National data on Aboriginal and Torres Strait Islander people are not available for the pre-vaccine period, but studies in the Northern Territory reported an incidence of between 270 and 530 per 100,000 in children aged <5 years.4,5 In contrast, the national rate for Aboriginal and Torres Strait Islander children in this age group in this reporting period was 5.6 per 100,000. However, while rates in other children have continued to decline in recent years, those in Aboriginal and Torres Strait Islander children have not, resulting in a widening disparity.

Data from most Indigenous populations worldwide have shown dramatic decreases in invasive Hib disease, but the rates remain higher than in corresponding non-Indigenous populations.6 Environmental and social deprivation, including household crowding and high smoking rates, are the most likely causes for this disparity and are the most commonly shared characteristics between Indigenous populations in developed countries. Studies have shown that Hib nasopharyngeal carriage continues in Aboriginal and Torres Strait Islander children in some areas despite high levels of vaccination.7 It has also been suggested that some Indigenous populations have an increased susceptibility to Hib disease as well as poor immune responses to immunisation. Genetic factors have been implicated in some settings,6 but in Aboriginal and Torres Strait Islander children, weaker immune responses occurred only after the first year of life, suggesting environmental causes were responsible for the poorer immune response.8

PRP-OMP vaccine has been preferred for Aboriginal and Torres Strait Islander children in Australia and American Indian children in the United States. It provides protection at an earlier age than other vaccines, and Aboriginal and Torres Strait Islander children are affected at an earlier age than other children.9 A resurgence of Hib disease was observed in Alaskan Native children following the replacement of a PRP-OMP vaccine with HbOC (Hib oligosaccharide CRM197), which then prompted a return to PRP-OMP vaccines in Alaska.10 The progressive withdrawal of PRP-OMP vaccines (3 doses) in Australia from 2005 to 2009, replaced by 4 doses of PRP-T, was due to an international shortage of PRP-OMP vaccine. While it is possible that higher disease rates in young infants could be a consequence of the later age of protection from PRP-T vaccine, it is also possible that higher immunogenicity of PRP-T vaccine will result in reduced carriage. Resurgence of Hib disease following use of PRP-T vaccine has not been reported from Canada11 or New Zealand,12 where this vaccine has been used for both Indigenous and non-Indigenous children. Vigilant surveillance and high vaccination coverage are particularly important in this setting, but substantial socioeconomic improvements remain imperative.