Vaccine Preventable Diseases and Vaccination Coverage in Aboriginal and Torres Strait Islander People, Australia, 2003 to 2006

Discussion

Disclaimer: Produced by the National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases and the Australian Institute of Health and Welfare on behalf of the Australian Government Department of Health and Ageing Published as a supplement to the Communicable Diseases Intelligence journal Volume 32, June 2008.

Page last updated: 30 June 2008

This is the second report to provide detailed data on VPDs and vaccination coverage in Aboriginal and Torres Strait Islander people. More detailed analysis and presentation of data has been made possible by improvements to the ACIR, NATSIHS and hospitalisation data.

Vaccination coverage

Vaccination coverage for the standard vaccines nationally is 6%–8% lower in Indigenous compared with non-Indigenous infants at 12 months of age, largely due to the higher prevalence of delayed vaccination in Indigenous children. By 24 months of age, that difference has disappeared and coverage is over 90%.

In adults, where universal vaccination programs are in place (for those aged 65 years or more, influenza and pneumococcal vaccine), there is no significant difference in national coverage between Indigenous and non-Indigenous people. Where these universal programs have achieved high coverage, the previously seen coverage gradient in Aboriginal and Torres Strait Islander people from higher in remote areas to lower in urban areas appears to no longer be the case.

However, for vaccines or age groups where vaccination is targeted only at Aboriginal and Torres Strait Islander people, such as hepatitis A, 23vPPV for infants, or influenza and 23vPPV in adults aged less than 65 years, coverage is markedly lower, although still higher than in the non-target population. Along with lower coverage, the gradient from remote to urban is still evident for the adult vaccines.

Impact

The achievement of high coverage for standard vaccines has had a substantial positive impact on the health of Aboriginal and Torres Strait Islander people. A number of diseases which have been eliminated from Australia by vaccination, or for which endemic transmission has been largely controlled, caused significant disease burdens in the past, and disproportionately affected Aboriginal and Torres Strait Islander people. The pre-vaccination impacts on Aboriginal and Torres Strait Islander people have been documented for some of these diseases, such as smallpox,91 measles,61 hepatitis B,50 and invasive Hib disease,92 while, for others, it can be assumed to be at least as severe as for the rest of the population, such as diphtheria, tetanus and poliomyelitis.

However, for some standard vaccines, high coverage has not been sufficient to control the disease. Pertussis epidemics continue to occur in Australia due to waning vaccine-induced immunity, and this is likely to continue until older Australians are immunised and/or an improved vaccine is developed. It seems likely that higher hospitalisation rates in Aboriginal and Torres Strait Islander infants are caused by a combination of more common delayed vaccination and generally poorer environmental living conditions.

Although Hib vaccine has resulted in a greater than 90% decrease in Hib disease, the few remaining cases occur at much higher rates in Aboriginal and Torres Strait Islander children. A similar situation has been reported in other indigenous populations that had high pre-vaccination rates of disease and this may be less marked in recent years.32,93 However, more research is needed to clarify the potential roles of continued carriage, delayed vaccination and vaccine failure.

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For IPD and meningococcal disease, the universal vaccination programs have been very successful, but a greater proportion of cases in Aboriginal and Torres Strait Islander people are of serotypes not prevented by the vaccine. There have historically been much higher rates of IPD in Indigenous compared with non-Indigenous children and adults.94,95 There has been a substantial impact of the 7vPCV vaccine on disease rates, but higher rates remain in Aboriginal and Torres Strait Islander children, largely due to serotypes not contained in the vaccine. Hoped for impact on the more common manifestations of pneumococcal infection – non-bacteraemic pneumonia and otitis media – have been seen overseas but not in Australian Indigenous people. In the US, a post-vaccination increase has been observed in IPD due to serotypes not covered by the vaccine, and this has been most marked in Alaskan indigenous people.96 While there is no clear evidence of that in Australia so far, this needs to be closely monitored. New vaccines with broader IPD serotype coverage are likely to be available in the near future79,80 and may have an important role for Indigenous people. The impact of 23vPPV vaccination in the second year of life in preventing IPD and the emergence of non-7vPCV serotypes also needs further examination.

The impact of the universal meningococcal C vaccination program from 2003 is evident in data in this report. Although serogroup C meningococcal disease has seriously affected Indigenous people in the past,66,97 currently a greater proportion of disease in Indigenous, compared with non-Indigenous, people is serogroup B and therefore not covered by the vaccine. A serogroup B vaccine with broad coverage of relevant subtypes would be valuable.

Vaccination programs targeted specifically at Indigenous people are often necessary where large disparities in disease burden exist and the cost-effectiveness of vaccination of non-Indigenous people is less clear. Data in this report show that coverage is consistently lower for these programs.

In young Indigenous adults, the extent of the disease burden from IPD, pneumonia and influenza, and the substantial disparity in comparison with non-Indigenous people of the same age, are evident. The impact of adult vaccination on Aboriginal and Torres Strait Islander adults has not yet been clearly established, but this may be due to the fact that the vast majority of disease occurs in younger adults, in whom coverage has been low. Expansion of the age-based recommendations for 23vPPV down to 30 years, and for influenza vaccine to all Aboriginal and Torres Strait Islander adults, may have an impact if funded and implemented. Unfunded recommendations present a challenge to service providers to maximise the potential benefits from vaccination in these age groups.

High hospitalisation rates for influenza in infants, significantly higher for Indigenous compared with non-Indigenous infants, suggest a possible role for vaccination. Universal infant vaccination is in place in the US and Canada. Either a universal or targeted program may be justified in Australia, and this is currently under consideration by ATAGI.