Vaccine preventable diseases and vaccination coverage in Aboriginal and Torres Strait Islander people, Australia 2006–2010

2.4 Seasonal influenza, pandemic influenza and pneumonia

Page last updated: 19 December 2013

Influenza is an acute respiratory tract infection caused mainly by influenza type A and type B viruses.3 Acute febrile influenza illness can range from mild to debilitating, and in some cases may become exacerbated by a variety of secondary complications. The risk of developing serious complications is higher at both extremes of age and also in those with certain underlying conditions. The most common serious complications include exacerbation of underlying chronic pulmonary and cardiopulmonary diseases, such as chronic obstructive pulmonary disease, asthma and congestive heart failure, as well as development of pneumonia (primary viral or bacterial) which may be fatal.3 Vaccination against the disease is complicated by the capacity of influenza A and B viruses to undergo gradual antigenic change in their two surface antigens, haemagglutinin (HA) and neuraminidase (NA).3 Antigenic shift in influenza viruses can cause pandemics which are associated with higher rates of illness and death.3

Relevant vaccine history

1986

  • Seasonal influenza vaccination recommended for individuals at risk of complications or death from influenza: persons >65 years of age, persons with chronic debilitating disease, persons receiving immunosuppressive therapy, persons engaged in medical and health services.

1994

  • Seasonal influenza vaccination recommended for Aboriginal and Torres Strait Islander people aged >50 years.

1999

  • Seasonal influenza vaccine funded nationally for all Australians aged >65 years and Aboriginal and Torres Strait Islander people aged >50 years or aged 15–50 years with medical risk factors.

2009

  • Pandemic influenza A (H1N1) 2009 vaccine registered, recommended and funded: 1 dose for children aged ≥10 years and adults; and 2 doses for children aged 6 months to ≤9 years.

2010

Seasonal influenza vaccine funded for:

  • all Aboriginal and Torres Strait Islander people aged ≥15 years
  • all persons aged ≥6 months with medical conditions predisposing to severe influenza for whom influenza vaccination is recommended
  • pregnant women.

Key points

Severe illness due to seasonal influenza infection is more common in Aboriginal and Torres Strait Islander people; this was also the case with the 2009 pandemic influenza A (H1N1). This is thought to be due to a higher prevalence of risk factors for severe disease in Aboriginal and Torres Strait Islander people. Improvement in vaccination coverage should be a priority.

Top of page

Disease trends

Influenza hospitalisation data are presented for the period 1999–2010 for the Northern Territory, Queensland, South Australia and Western Australia. Time trends in figures are presented by calendar instead of financial years so that each data point includes one full winter season. Data for notifications are not presented due to the low level of completeness of the Indigenous status field in notification records.

Influenza hospitalisation rates for Aboriginal and Torres Strait Islander people aged ≥50 years declined somewhat after the first year of funded vaccination (1999) but confidence intervals for individual years overlapped. Hospitalisation rates in Aboriginal and Torres Strait Islander people in 2005–2010 are still 4.6 times higher than the rates in other people. The peaks in 2003 and 2007 (Figure 2.4.1) reflect more severe influenza seasons nationally. The spike in 2009 coincides with the influenza A (H1N1) pandemic. A much higher impact of the influenza pandemic was noted in Aboriginal and Torres Strait Islander people than in other people (Figure 2.4.1). A more detailed analysis of enhanced data on pandemic influenza A (H1N1) 2009 infection has been included below as a subsection in this chapter.

Figure 2.4.1: Influenza* hospitalisation rates, selected Australian states, 1999 to 2009, by age group and Indigenous status

Figure 2.4.1: is a line chart showing the Influenza hospitalisation rates, 1999 to 2009, by age group and Indigenous status. A link to a text description follows.

* The ICD-10-AM codes used to identify influenza hospitalisations were: J09 (influenza due to certain identified influenza viruses), J10 (influenza due to identified influenza virus) and J11 (influenza, virus not identified).

† Jurisdictions with satisfactory data quality over the whole time period; see Appendix A (Northern Territory, Queensland, South Australia, Western Australia).

‡ Hospitalisations where the date of separation was between 1 January 1999 and 31 December 2009.

Text description of Figure 2.4.1 (TXT 1 KB)

Top of page

Hospitalisation rates for influenza and pneumonia combined (Figure 2.4.2) are more than 20 times the rates for influenza alone, with a large difference between Aboriginal and Torres Strait Islander and other people, and little change over time. ‘Influenza and pneumonia’ is, however, a non-specific diagnosis with multiple aetiologies.

Figure 2.4.2: Influenza and pneumonia* hospitalisation rates and 95% confidence intervals, selected Australian states, 2000 to 2009, by Indigenous status

Figure 2.4.2: is a line chart showing the Influenza and pneumonia* hospitalisation rates and 95% confidence intervals. A link to a text description follows.

* The ICD-10-AM codes used to identify hospitalisations were J09–J18 (Influenza and/or pneumonia).

† Jurisdictions with satisfactory data quality over the whole time period; see Appendix A (Northern Territory, Queensland, South Australia, Western Australia).

‡ Hospitalisations where the date of separation was between 1 January 2000 and 31 December 2009. Rates are age-standardised to the Australian Bureau of Statistics Australian population estimates for 2006.

Text description of Figure 2.4.2 (TXT 1 KB)

Top of page

Hospitalisation data for influenza are presented for six jurisdictions (all except Tasmania and the Australian Capital Territory) by financial year for the period July 2005 to June 2010. A total of 22,998 hospitalisations for influenza were recorded during this reporting period, of which 2,245 (10.8%) were reported in Aboriginal and Torres Strait Islander people. Rates in Aboriginal and Torres Strait Islander people were consistently higher than in other people across all age groups (Table 2.4.1). The highest hospitalisation rates were seen in Aboriginal and Torres Strait Islander children in the 0–4 years age group (209.7 per 100,000) followed by those in the ≥50 years age group (136.1 per 100,000). The overall Indigenous to non-Indigenous rate ratio was 4.6:1.

There were 235 deaths reported from the five jurisdictions (New South Wales, the Northern Territory, Queensland, South Australia and Western Australia) for the period 2006–2010 with influenza as the underlying cause. Of those deaths, 14 were reported in Aboriginal and Torres Strait Islander people; there were no deaths in the 0–4 years age group, 6 in the 5–49 years age group, and 8 in the ≥50 years age group. There were 7,879 deaths reported with influenza or pneumonia as the underlying cause, of which 183 were reported in Aboriginal and Torres Strait Islander people; 17 in the 0–4 years age group, 68 in the 5–49 years age group and 98 in the ≥50 years age group. There were 341 deaths reported with influenza as the underlying or a contributing cause (20–23 in Aboriginal and Torres Strait Islander people) and 58,268 deaths with pneumonia as the underlying or a contributing cause (1,120 in Aboriginal and Torres Strait Islander people). The ABS provides ranges when absolute numbers of deaths are low.

Table 2.4.1: Influenza hospitalisations, selected Australian states, 2005 to 2010, by age group and Indigenous status
Age group
(years)
Indigenous status Hospitalisations* (2005–2010)
n Rate Rate ratio

* Hospitalisations (New South Wales, Northern Territory, Queensland, South Australia, Victoria, Western Australia only) where the date of separation was between 1 July 2005 and 30 June 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
657
209.7
2.9§
Other
4,435
72.0
5–14
Indigenous
238
38.4
2.6§
Other
1,876
14.9
15–24
Indigenous
264
53.3
3.4§
Other
2,178
15.9
25–49
Indigenous
678
85.2
5.4§
Other
5,603
15.7
>50
Indigenous
408
136.1
6.3§
Other
6,661
21.6
All ages
Indigenous
2,245
97.2
4.6§
Other
20,753
21.0

Top of page

Pandemic influenza A (H1N1) 2009

Analysed data for this subsection on pandemic influenza in Aboriginal and Torres Strait Islander people was provided by the Australian Government Department of Health and Ageing (Table 2.4.2).27 During the 2009 influenza pandemic, cases of laboratory-confirmed influenza A (H1N1) 2009 infections, hospitalisations and deaths were notified to state and territory health departments, which then notified the National Incident Room (NIR) using NetEpi, a web-based outbreak case reporting system. Nationally collected NetEpi data is used here to describe the severity and mortality of pandemic influenza A (H1N1) during 2009 in Aboriginal and Torres Strait Islander Australians.

Table 2.4.2: Pandemic influenza A (H1N1) 2009 infections, Australia, 2009, by Indigenous status
Indigenous Other Rate ratio
n Rate* Median age
(95% CI)
n Rate* Median age
(95% CI)

* Age-standardised rate per 100,000 population, standardised to 2006 non-Indigenous population.

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

Source: H1N1 2009 infections in Australia’s Indigenous population in 2009, DOHA27

Notifications
4,063
892.7
18 (18–19)
33,620
173.3
21 (21–22)
5.2
Hospitalisations
830
182.4
31 (28–34)
4,163
21.5
31 (29–32)
8.5
ICU admissions
77
16.9
42 (36–44)
412
2.1
43 (40–47)
7.9
Deaths
23
5.1
50 (42–56)
168
0.9
50 (47–55)
5.8

During 2009, a total of 37,683 notifications of pandemic influenza A (H1N1) 2009 were reported to NetEpi (Table 2.4.2). Of those, 11% (4,063/37,683) were listed as Aboriginal and Torres Strait Islander, 50% (18,832/37,683) were non-Indigenous, and for 39% (14,788/37,683) Indigenous status was missing or unknown. Cases with unknown or missing Indigenous status were included in the ‘other’ group for further analysis. Other notifications peaked in the 15–19 years age group and then declined with increasing age. For notifications in Aboriginal and Torres Strait Islander people there was no clear trend by age, the highest rate was in the 50–54 years age group (Figure 2.4.3).

Of the total 37,683 notified cases reported to NetEpi, 4,993 (13.3%) were hospitalised, with 17% (830/4,993) of these reported as Aboriginal and Torres Strait Islander and 83% (4,163/4,993) as other (Table 2.4.2). Twenty per cent (830/4,063) of all Aboriginal and Torres Strait Islander notifications and 12.4% (4,163/33,620) of other notifications were hospitalised. In Aboriginal and Torres Strait Islander people, the highest rate of hospitalisation (395 per 100,000) was in the 50–54 years age group; in other people, the highest rate (58 per 100,000) was in the <5 years age group. The age-standardised Indigenous to non-Indigenous rate ratio for admissions to hospital was 8.5.

Figure 2.4.3: Pandemic influenza A (H1N1) 2009 infection reporting rates to NetEpi, Australia, 2009, by age group

Figure 2.4.3: is a line chart showing the pandemic influenza A (H1N1) 2009 infection reporting rates to NetEpi, Australia, 2009, by age group. A link to a text description follows.

Source: H1N1 2009 infections in Australia’s Indigenous population in 2009, DOHA27

Text description of Figure 2.4.3 (TXT 1 KB)

Top of page

A total of 489 influenza A (H1N1) 2009 cases notified to NetEpi were admitted to an intensive care unit (ICU) during 2009, representing 1.3% of all notifications (Table 2.4.2). Victoria and Queensland used the Australian and New Zealand Intensive Care Study (ANZICS) to record ICU admissions and so are not represented in this analysis for ICU admissions. The highest rate of ICU admissions for Aboriginal and Torres Strait Islander people was in the 55–59 years age group with 75.6 admissions per 100,000. For other people, the highest ICU admission rate was in the 50–54 years age group, but it was much lower at 4 per 100,000. The age-standardised Indigenous to non-Indigenous rate ratio for ICU admissions was 7.9.

Pregnant women have also been identified as an important high priority group because of the increased risk of severe health outcomes from influenza.28 Of the 37,683 notifications for influenza A (H1N1) 2009, 568 (1.5%) were in pregnant women, with 10% (55/568) of those being in Aboriginal and Torres Strait Islander women. Of pregnant women who were notified with influenza A (H1N1) 2009 infection, 53% (300/568) were hospitalised and 15% (44/300) of those hospitalised were Aboriginal and Torres Strait Islander women. Among women aged 20–34 years, 37% of those requiring hospitalisation and 33% of those requiring ICU admission were pregnant.

Metabolic disorders, diabetes, cardiac conditions, respiratory conditions and obesity were more likely to be found as comorbidities in Aboriginal and Torres Strait Islander people notified with influenza A (H1N1) 2009 than in other people. Aboriginal and Torres Strait Islander people with renal failure and diabetes were more than twice as likely as other people with those conditions to be notified, hospitalised and admitted to ICU with influenza A (H1N1) 2009. Of Aboriginal and Torres Strait Islander people who were hospitalised, almost 50% had at least one comorbidity.

There were a total of 191 deaths from influenza A (H1N1) infection during 2009, representing 0.5% of all notifications (Table 2.4.2). Of those, 23 (12%) were in Aboriginal and Torres Strait Islander people and 168 (88%) were in other people. The age-standardised Indigenous to non-Indigenous rate ratio was 5.8.

Top of page

Comment

The new influenza A (H1N1) virus which emerged among humans in Mexico in early 2009 generated the first influenza pandemic of the 21st century. The clinical spectrum of disease, severity of illness and the risk factors for complications among confirmed cases of influenza A (H1N1) 2009 illness in Australia were consistent with reports from overseas and were similar to the disease profile of seasonal influenza.29 The underlying medical conditions associated with pandemic influenza A (H1N1) 2009 and seasonal influenza illnesses diagnosed in the community were also similar. The main differences were that, for pandemic influenza A (H1N1) 2009, there was a shift to a younger age distribution and an even greater risk associated with pregnancy.29 The reduced susceptibility of the elderly to pandemic influenza A (H1N1) 2009 resulted in a smaller number of influenza-related deaths in that age group than in most other influenza seasons.28

Australian public health agencies identified groups vulnerable to poor outcomes from pandemic influenza A (H1N1) 2009 infection and targeted them for priority receipt of antiretroviral treatment and vaccination. These groups were Aboriginal and Torres Strait Islander people, pregnant women, and people with morbid obesity or serious underlying medical conditions.28 The public health response for Aboriginal and Torres Strait Islander people was facilitated by establishing an Indigenous Influenza Network which held regular teleconferences to coordinate the response.30 Some reports documenting local efforts to target Aboriginal and Torres Strait Islander people have been published.31,32

Increased risks of infection, hospitalisation and death due to pandemic influenza A (H1N1) 2009 in Indigenous populations have been reported in many countries including the United States, Canada, New Zealand and Australia,33-35 and are also presented in this report. The occurrence of more severe forms of disease has been attributed to a higher susceptibility and prevalence of comorbidities among Indigenous people.33,34 Diseases including cardiovascular disease, diabetes and chronic respiratory disease are responsible for up to 70% of the observed health gap between Aboriginal and Torres Strait Islander and other Australians.36 However, there is also evidence of an increased risk of exposure to the virus,37 as well as higher hospitalisation rates in Aboriginal and Torres Strait Islander people than in others with the same risk factor.27 A highly mobile population and crowded living conditions are also thought to be risk factors for increased exposure to influenza and other viruses. Other factors causing reduced resilience may also be present in Aboriginal and Torres Strait Islander people.

Reports have indicated that uptake of vaccination against pandemic influenza A (H1N1) 2009 was suboptimal in the general population, at-risk groups, pregnant women and health professionals in most countries.38 For Australians of all ages, the vaccination coverage was around 20% for Aboriginal and Torres Strait Islander people and 21% for other people.39 However, this sole national estimate for Aboriginal and Torres Strait Islander people was from a small subset in a national telephone survey. No more detailed breakdowns are available, and there are limitations around using crude telephone surveys in this population with poorer telephone access.40 Other estimates are limited to Western Australia (20%)41 and the Northern Territory (41%).37 It is therefore difficult to evaluate the success of measures to prioritise Aboriginal and Torres Strait Islander people.

Seasonal influenza still remains an issue in vulnerable populations. The data presented here indicate that seasonal influenza rates continue to be higher in Aboriginal and Torres Strait Islander people than in other people, including in the ≥50 year age group, in which vaccine has been funded for Aboriginal and Torres Strait Islander people since 1999. Since 2010, seasonal influenza vaccine has been funded for all Aboriginal and Torres Strait Islander people aged ≥15 years. This broadening of the vaccination program has the potential to result in a further reduction in the disease burden of seasonal influenza in Aboriginal and Torres Strait Islander people. However, a scarcity of data is an obstacle to program management for seasonal influenza vaccination; there are no coverage estimates for Aboriginal and Torres Strait Islander adults for the first 3 years of this program (also discussed in the ‘Vaccination coverage’ chapter of this report). Development of strategies to monitor and increase vaccine uptake in high-risk groups should be a priority in tackling seasonal influenza, as well as in preparedness for future pandemics.