Vaccine Preventable Diseases and Vaccination Coverage in Australia, 2003 to 2005

Trends in vaccination coverage estimates from the ACIR

Disclaimer: This is the fourth report on vaccine preventable disease and vaccination coverage in Australia, and is 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 31, June 2007.

Page last updated: 20 July 2007

The trends in childhood vaccination coverage in Australia for three doses of DTPa, OPV and two or three doses of Hib and Hep B assessed at 12 months of age, and for three or four doses of DTPa (according to the vaccine schedule in use), two or three doses of Hib and Hep B, three doses of OPV, and one dose of MMR assessed at 24 months, and for two doses of MMR, four or five doses of DTPa, and four doses of OPV assessed at 72 months of age are shown in Figure 53. Coverage was calculated for 36 consecutive three-month cohorts born from 1 January 1996 to 31 December 2004. For all vaccines due by one year of age, coverage estimates increased steadily from 75% for the first cohort, to 90% by the thirty-sixth cohort, assessed on 31 December 2005. For all vaccines due by 24 months of age, coverage estimates also increased steadily from 64% for the first cohort to 92.1% by December 2005. Coverage estimates for all vaccines due by 72 months of age were first reported in Communicable Diseases Intelligence in 2002, and have also increased steadily from 80.6% in early 2002 to 83.8% in late 2005.

Coverage estimates for the 24-month age group had a noticeable increase in September 2003, largely as a result of a more liberal definition of completeness following the removal of the fourth dose of DTPa (due at 18 months) from the immunisation schedule from this quarter onwards. Coverage estimates for the 12-month age group have, however, remained steady over the past five years fluctuating around the 91% level. With up to 3% of Australian parents not immunising their children because they object to, disagree with, or are concerned about immunisation,296 it will be difficult for 'fully immunised’ coverage estimates to exceed 95%, especially as the reporting of immunisation encounters is still not totally complete due to poor reporting by some providers and late immunisation by some parents.

Figure 53. Trends in vaccination coverage estimates from the Australian Childhood Immunisation Register for 12, 24 and 72 month olds*

Figure 53. Trends  in vaccination coverage estimates from the Australian Childhood Immunisation  Register for 12, 24 and 72 month olds

Source: Australian Childhood Immunisation Register.

* By three-month birth cohorts born between 1 January 1996 and 31 December 2004. Coverage assessment date was 12 months, 24 months or 72 months after the last birth date of each cohort.

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Vaccines scheduled in the first year of life

Differences between states and territories in estimates of the proportion of children classified as 'fully immunised’ are shown in Figure 54. 'Fully immunised’ coverage remained reasonably stable over the three year assessment period for all jurisdictions with almost all of them reaching the Immunise Australia Program target of 90% coverage for the first milestone vaccines. Coverage in the Northern Territory and the Australian Capital Territory fluctuated noticeably over the whole period. Significant changes in coverage in jurisdictions like the Northern Territory and the Australian Capital Territory, who have relatively small populations, are likely to be the result of small numbers of unimmunised children having large impacts on the coverage percentages.

Figure 54. Trends in vaccination coverage estimates, by jurisdiction: children 'fully immunised’ at the age of 12 months*

Figure 54. Trends  in vaccination coverage estimates, by jurisdiction: children fully immunised  at the age of 12 months

Source: Australian Childhood Immunisation Register

* By three-month birth cohorts born between 1 January 2002 and 31 December 2004. Coverage assessment date was 12 months after the last birth date of each cohort.

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The trends in childhood vaccination coverage in Australia for individual vaccines (DTPa, OPV, Hib and Hep B assessed at 12 months) are shown in Figure 55, calculated for 12 consecutive three-month cohorts born from 1 January 2002 to 31 December 2004. Coverage estimates for all vaccines remained stable throughout the 2001 to 2003 period, hovering around the 92% to 95% mark. Coverage for the Hib and Hep B vaccines is greater than DTPa and OPV coverage largely due to the spurious effect of the change in the immunisation schedule in mid 2000, altering the algorithm used to calculate coverage at 12 months of age where a record of two doses of Hib and Hep B on the ACIR is enough for a child to be considered 'fully immunised’.

Figure 55. Trends in vaccination coverage estimates for individual vaccines: children vaccinated with DTPa, OPV, HepB and Hib at the age of 12 months*

Figure 55. Trends  in vaccination coverage estimates for individual vaccines: children vaccinated  with DTPa, OPV, HepB and Hib at the age of 12 months

Source: Australian Childhood Immunisation Register.

* By three-month birth cohorts born between 1 January 2002 and 31 December 2004. Coverage assessment date was 12 months after the last birth date of each cohort.

Figure 56 presents a map of immunisation coverage at 12 months of age in Australia by Australian Bureau of Statistics (ABS) Statistical Subdivision. The map demonstrates that, whilst coverage is greater than 90% in almost all jurisdictions, there exist a significant number of areas that have low levels of coverage, below 90%, and even below 85% in a few areas such as Richmond-Tweed and Lismore (NSW).

Figure 56. Immunisation coverage for 'fully immunised’ at 12 months of age, Australia, December 2005

Figure 56. Immunisation  coverage for fully immunised at 12 months of age, Australia, December 2005

The timeliness of the third dose of DTPa, due at six months of age, by jurisdiction, for the cohort born 1 January 2004 to 31 March 2004 is shown in Figure 57. Timeliness varied by jurisdiction, with children in Western Australia and the Northern Territory experiencing greater vaccination delay, and children in the Australian Capital Territory being more on time for their third dose of DTPa. However, whilst timeliness varies between jurisdictions, eventually all jurisdictions catch up by 12 months of age (Figure 57).297

Figure 57. Timeliness of the third dose of DTPa (due at 6 months of age), by jurisdiction – cohort born 1 January 2004–31 March 2004

Figure 57. Timeliness  of the third dose of DTPa (due at 6 months of age), by jurisdiction - cohort  born 1 January 2004-31 March 2004 Top of page

Vaccines scheduled in the second year of life

Differences between states and territories in estimates of the proportion of children classified as 'fully immunised’ at 24 months of age are shown in Figure 58. 'Fully immunised’ coverage at 24 months of age for consecutive cohorts increased markedly for all jurisdictions between the June and September quarters in 2003, mainly due to the removal of the fourth dose of DTPa vaccine at 18 months from the immunisation schedule in September 2003. The coverage assessment for the 24-month cohort now excludes the requirement for the 18-month dose of DTPa. There was significant variation between the jurisdictions across the three-year period with Tasmania, the Northern Territory, South Australia and Victoria consistently having higher coverage levels than the other four jurisdictions. However, by the end of 2005, all jurisdictions had reached the 90% coverage target.

Figure 58. Trends in vaccination coverage estimates, by jurisdiction: children 'fully immunised’ with DTPa, OPV, HepB, Hib and MMR at the age of 24 months*

Figure 58. Trends  in vaccination coverage estimates, by jurisdiction: children fully immunised  with DTPa, OPV, HepB, Hib and MMR at the age of 24 months

Source: Australian Childhood Immunisation Register.

* By three-month birth cohorts born between 1 January 2001 and 31 December 2003. Coverage assessment date was 24 months after the last birth date of each cohort.

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The trends in childhood vaccination coverage in Australia for individual vaccines (DTPa, OPV, Hib, Hep B and MMR assessed at 24 months) are shown in Figure 59, calculated for 12 consecutive three-month cohorts born from 1 January 2001 to 31 December 2003. As discussed previously, there was a significant increase in coverage for DTPa at 24 months of age during 2003 due to the removal of the fourth dose of DTPa from the schedule. For most of the three-year period, Hep B coverage was higher than for all other vaccines (most likely due to the coverage algorithm accepting two or three doses of Hep B as an indication of fully immunised status), hovering just below 96%, whilst coverage at 24 months of age was lowest for the MMR and Hib vaccines. However, there has been a real lack of movement in coverage for any of the vaccines assessed at this age, as evidenced by the very flat curves for all vaccines.

Figure 59. Trends in vaccination coverage estimates for individual vaccines: children vaccinated with DTPa, OPV, HepB, Hib and MMR at the age of 24 months*

Figure 59. Trends  in vaccination coverage estimates for individual vaccines: children vaccinated  with DTPa, OPV, HepB, Hib and MMR at the age of 24 months

Source: Australian Childhood Immunisation Register.

* By three-month birth cohorts born between 1 January 2001 and 31 December 2003. Coverage assessment date was 24 months after the last birth date of each cohort.

Figure 60 presents a map of immunisation coverage at 24 months of age in Australia by Australian Bureau of Statistics (ABS) Statistical Subdivision. The map demonstrates, as with Figure 56, that whilst coverage is over 90% in all jurisdictions, there exist many small areas within jurisdictions that have levels of coverage below 90%, such as regional areas in Western Australia and New South Wales.

Figure 60. Immunisation coverage for 'fully immunised’ at 24 months of age, Australia, December 2005

Figure 60. Immunisation  coverage for fully immunised at 24 months of age, Australia, December 2005 Top of page

The timeliness of the first dose of MMR by jurisdiction for the cohort born 1 January 2003 to 31 March 2003 is shown in Figure 61. As with the third dose of DTPa, the timeliness of the first dose of MMR varied by jurisdiction, with children in Western Australia and the Northern Territory again experiencing greater vaccination delay, and children in Tasmania being more on time for this vaccine dose. Again, whilst timeliness of MMR vaccination varies between jurisdictions, eventually all jurisdictions catch up by 18 months of age (Figure 61).297

Figure 61. Timeliness of the first dose of MMR (due at 12 months of age), by jurisdiction – cohort born 1 January 2003–31 March 2003

Figure 61. Timeliness  of the first dose of MMR (due at 12 months of age), by jurisdiction – cohort  born 1 January 2003 to 31 March 2003 Top of page

Vaccines given at 4–5 years of age

Differences between states and territories in estimates of the proportion of children classified as 'fully immunised’ by 72 months of age are shown in Figure 62. 'Fully immunised’ coverage increased only slightly over the three year assessment period for most jurisdictions, with some jurisdictions experiencing a greater increase than others, and a couple (Queensland and Western Australia) experiencing an overall slight decrease. Coverage was highest in Victoria and the Australian Capital Territory.

Figure 62. Trends in vaccination coverage estimates, by jurisdiction: children 'fully immunised’ with DTPa, OPV and MMR at the age of 72 months *

Figure 62. Trends  in vaccination coverage estimates, by jurisdiction: children fully immunised  with DTPa, OPV and MMR at the age of 72 months

Source: Australian Childhood Immunisation Register.

* By three-month birth cohorts born between 1 January 1997 and 31 December 1999. Coverage assessment date was 72 months after the last birth date of each cohort.

The trends in childhood vaccination coverage in Australia for individual vaccines (DTPa, OPV and MMR assessed at 72 months) are shown in Figure 63, calculated for 12 consecutive three-month cohorts born from 1 January 1997 to 31 December 1999. Coverage for all three vaccines was almost identical and remained steady across the whole period hovering around 85% with very little change.

Figure 63. Trends in vaccination coverage estimates for individual vaccines: children vaccinated with DTPa, OPV and MMR at the age of 72 months*

Figure 63. Trends  in vaccination coverage estimates for individual vaccines: children vaccinated  with DTPa, OPV and MMR at the age of 72 months

Source: Australian Childhood Immunisation Register.

* By three-month birth cohorts born between 1 January 1997 and 31 December 1999. Coverage assessment date was 72 months after the last birth date of each cohort.

Figure 64 presents a map of immunisation coverage at 72 months of age in Australia by Australian Bureau of Statistics (ABS) Statistical Subdivision. The map demonstrates that coverage for this age group, compared with other milestones, is below target levels in many areas of Australia, and is less than 85% in a majority of areas. However, there are a few areas in regional Victorian and Western Australia where coverage has reached levels achieved at 12 and 24 months of age.

Figure 64. Immunisation coverage for 'fully immunised’ at 72 months of age, Australia, December 2005

Figure 64. Immunisation  coverage for fully immunised at 72 months of age, Australia, December 2005 Top of page

Comment

Australia is uniquely well placed to monitor immunisation coverage and timeliness of immunisation routinely and regularly because of its universal national childhood immunisation register, the ACIR, the only national register of its kind in the world. The ACIR records immunisation data on all children under the age of 7 years enrolled in the Australian universal health insurance scheme, Medicare, and constitutes a nearly complete population register, as approximately 99% of the 250,000 children born each year are registered with Medicare by 12 months of age.

Estimates of vaccination coverage in Australia for all jurisdictions have increased steadily since the ACIR commenced in 1996 but less so in recent years. There have been increases in coverage for 12 month olds, 24 month olds and 72 month olds, with 'fully immunised’ coverage for 12 and 24 month olds reaching the Immunise Australia Program target of 90% coverage for the first and second milestone vaccines.

The ACIR is now likely to be performing at close to its maximum achievable capacity in terms of data administration, following the impact of the General Practitioner Immunisation Incentive Scheme, parental incentives, the recording of overseas-given immunisations on the ACIR and data cleaning initiatives such as the ACIR Field Officers. Limitations of the ACIR, related to reliance on provider notification and the currency of Medicare registration, mean that official estimates of coverage are unlikely to rise significantly above current levels, especially at the 12 and 24 month old milestones, unless mechanisms are put in place to further improve notification to the ACIR. Increases in actual coverage will also be difficult to achieve from this point, as there are probably 2%–3% of parents who are officially opposed to immunisation and a further slightly larger percentage that are opposed to immunisation but who do not object through official channels.

To maintain the current high levels and to achieve further increases in coverage, especially in the 72 month old group, efforts need to be directed at improving reporting by providers (and subsequent data cleaning), and at immunisation of the small group of children now not up to date with their immunisations. The latter will require carefully targeted initiatives, which may include efforts to further improve access to services for disadvantaged groups and specific educational initiatives for those parents and providers concerned about contraindications to immunisation.

Analysis of age appropriateness (timeliness) of childhood immunisation in Australia is not routinely undertaken using ACIR data, with regular reports limited to immunisation coverage for scheduled vaccines at the age milestones of 12, 24 and 72 months for each three-month birth cohort.295 With coverage estimates for most vaccines reaching levels required for herd immunity, the next benchmark for program success is timeliness, which can be regularly reported with an immunisation register, in contrast to the intermittent reports possible from national surveys. In addition, failure to commence the immunisation schedule on time has been shown to be a powerful predictor of failure to complete it.298,299 Measurement of timeliness should be incorporated into routine monitoring of the success of immunisation program delivery in countries with high levels of immunisation coverage.

It should be noted that there are several national, publicly funded, targeted immunisation programs for which systematically collected data on vaccine coverage are not currently available or published. These include meningococcal, pneumococcal and varicella vaccines for infants, Hep B vaccine for adolescents, dTpa vaccine for adolescents, MMR vaccine for 18–30 year olds, influenza and pneumococcal vaccines for Aboriginal and Torres Strait Islander persons over 50 years of age and influenza vaccine for persons over the age of 64 years. While data are available from surveys in local subpopulations91 or national special purpose surveys and studies110,111,300,301 for three of these programs, lack of widely applicable data inhibits planning and evaluation at the regional and national level. As the number and scope of immunisation programs increases, extension of the ACIR to collect data for some or all of the other age groups targeted by vaccines merits active consideration.

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