The Australian Childhood Immunisation Register (ACIR)
The Health Insurance Commission (HIC) provides quarterly reports on childhood immunisation coverage from the ACIR.
Prevenar (PCV7) coverage in Indigenous children
In 2001, a publicly funded pneumococcal conjugate vaccine (7vPCV) program commenced for Aboriginal and Torres Strait Islander children under 2 years. At present, there is very little knowledge about uptake of 7vPCV vaccine amongst Aboriginal and Torres Strait Islander children. This study examined the rollout and use of 7vPCV vaccine in Australia and estimated immunisation coverage for Indigenous children at the age of 12 months for 7vPCV vaccine. For all jurisdictions except the Northern Territory and Western Australia, where it has remained reasonably constant, estimated coverage increased over the most recent birth cohorts but was still less than 50% for all States except the Northern Territory Queensland, and Western Australia. This study provides the first national measure of 7vPCV immunisation coverage among Indigenous children in Australia. With the likely improvement over time in the recording of 7vPCV vaccinations and Indigenous status on the ACIR, the validity of coverage estimates is likely to increase. (Reference)
National vaccination coverage
Official immunisation coverage estimates reported using data from the ACIR are known to be underestimates. A number of studies have shown that a proportion of children identified by the Register as being un-immunised are actually completely immunised. The NCIRS was commissioned by the Department of Health and Ageing to undertake a study to measure how much underestimation exists when calculating immunisation rates for different age groups using data from the Register.
As two means-tested benefits to parents are linked to the immunisation status of children, the Commonwealth were also interested in assessing the impact of some of these incentives on parents decisions to immunise.
In all, the study had 5 components:
- To measure the difference in immunisation coverage estimates reported by parents compared to that documented in the ACIR at 12 months and 24 months, and to assess the level of under-reporting to the ACIR by providers.
- To assess the validity of the third-dose assumption that is used in coverage calculations.
- To determine the impact of the maternity allowance and child care benefit on immunisation coverage estimates.
- To assess the reasons why ACIR-reported immunisation coverage estimates are consistently low in inner urban areas of capital cities in Australia. More specifically, to what extent is coverage low because of parental compared with provider factors?
- To determine coverage of the second dose of MMR vaccine among 5-year-old children.
Results of this study are included in a report entitled "Immunisation Coverage: Australia 2001", which was published by the Commonwealth of Australia in May 2002. The pdf file is available here.
Mapping of immunisation coverage estimates in Australia
Maps of immunisation coverage in Australia have been created for each State at the Statistical Sub-Division (SSD) level for areas outside capital cities and at the Statistical Local Area (SLA) level for areas within capital cities. Maps of coverage levels at 12 and 24 months of age are provided for "fully immunised" coverage only. The coverage estimates were calculated using ACIR data. These maps are updated annually.
Impact of interventions
Register data are being used to evaluate the impact of the introduction of acellular pertussis vaccine and the financial incentives package.
Reference: Torvaldsen S, Hull BP, McIntyre PB. Using the Australian Childhood Immunisation Register to track the transition from whole-cell to acellular pertussis vaccines. Commun Dis Intell 2002;26(4):581-3 [Ref]
Evaluation of immunisation coverage for Aboriginal and Torres Strait Islander children
Using ACIR data we evaluated the immunisation status of children presumed to be Aboriginal or Torres Strait Islander based on the proxy marker of receipt of Pedvax Hib vaccine in regions outside the Northern Territory. This study provided the first national measure of immunisation status among Indigenous Australian children. The numbers of Aboriginal and Torres Strait Islander children estimated using our 'proxy method' were less than the number from the Australian Bureau of Statistics. Immunisation coverage at 12 months and 24 months was considerably lower among Aboriginal and Torres Strait Islander children than others. Among presumed Aboriginal and Torres Strait Islander children, coverage was significantly lower among those living in accessible areas than remote areas. (Reference 173)
MMR modelling
Data extracted from the ACIR were used to calculate measles, mumps, rubella (MMR) immunisation coverage estimates for children aged 24 months and 5 years for all Divisions of General Practice in Australia. ACIR coverage estimates were assumed to be 'worst case scenarios', representing the minimum possible immunisation coverage. Using the coverage estimates we calculated the susceptibility to measles in various age groups for various years in the future up to 2010. These susceptibility measures have then been used to calculate the reproductive number for Divisions of General Practice in Australia using methods developed by Nigel Gay from the UK Communicable Disease Surveillance Centre. A select number of Divisions (the poorly performing Divisions) have been provided with a graphical representation of this data, which provides them with an estimate of the number of susceptible children in their area and if and when an epidemic is likely.
Factors associated with low immunisation coverage
ACIR data provided an opportunity to develop explanatory models low immunisation coverage. ACIR coverage data at a postcode level were merged with ABS demographic data and ABS data containing indices of socioeconomic status, to enable construction of explanatory models describing immunisation coverage. Logistic regression analysis was used. Factors associated with lower immunisation uptake differed in rural and metropolitan areas. High levels of education and occupation and a high proportion of Aboriginal residents were significantly associated with lower coverage only in metropolitan postcodes. A high proportion of late starters to immunisation was the strongest single predictor of coverage and was important in rural and metropolitan postcodes. A high proportion of overseas-born persons and of general practitioner delivered immunisations was also associated with lower coverage in all areas. (Reference 20, Reference 48).
Evaluation of the Measles Control Campaign
See NCIRS Measles Control Campaign evaluation report.
Data quality indicators
The ACIR was established in 1996. An evaluation in late 1996 by the Human Capital Alliance showed that the Register had problems with data accuracy. NCIRS developed a number of data quality indicators for the Register, which allowed assessment of the ACIR's internal validity. These indicators were implemented by the Health Insurance Commission (HIC) as part of the routine reporting process, and were used in 1999 to show that data quality had improved over time.