Vaccine Preventable Diseases in Australia, 2005 to 2007

Executive summary

Page last updated: 24 December 2010

This report is the fifth in the biennial series of national reports on vaccine preventable diseases in Australia, bringing together the three most important national sources of routinely collected data about vaccine preventable diseases. This report adds data from January 2006 to December 2007 for notifications collected by the National Notifiable Diseases Surveillance System (NNDSS), from July 2005 to June 2007 for hospitalisation records in the AIHW National Hospital Morbidity Database, and from January 2005 to December 2006 for recorded deaths in the AIHW National Mortality Database. Jurisdictional notification data on two diseases for which national notification data are unavailable (varicella-zoster in South Australia and rotavirus in the Northern Territory) are also included.

The general trend towards improved control of disease and improved vaccination coverage is evident, particularly in the childhood years. Detailed results are presented in 16 individual chapters. The rates of notifications, hospitalisations and deaths for 10 more common diseases included in the National Immunisation Program (NIP) are summarised in the Table below.

Diseases with long-standing vaccination programs

During 2006–2007, there were no notified cases of diphtheria, and 1 imported case of poliomyelitis. A very low incidence of tetanus continued, affecting mainly older adults. A low incidence of invasive Haemophilus influenzae type b (Hib) disease (in young children), measles and rubella also continued in the 2 years under review. For measles, a relatively larger number of cases were reported in 2006, but this was predominantly associated with an outbreak in a community opposed to immunisation. Most, but not all, other outbreaks in the period were linked to overseas acquired cases. For rubella, despite low numbers of reported infections, 2 cases of congenital rubella syndrome were reported. While there are high levels of rubella immunity in the general population, immigrant women from some countries without an established rubella vaccination program, and Indigenous women in some communities, have been identified as having lower immunity and therefore being at higher risk of infection in pregnancy.

Table: Notification, hospitalisation and death rates of 10 vaccine preventable diseases over two periods,* Australia, 2002 to 2007

Disease
Notifications Hospitalisations Deaths
Average annual rate (per 100,000)
2003–2005
Average annual rate (per 100,000)
2006–2007
Average annual rate (per 100,000)
July 2002–
June 2005
Average annual rate (per 100,000)
July 2005–
June 2007
Average annual rate (per 100,000)
2003–2004
Average annual rate (per 100,000)
2005–2006
H. influenzae type b
(age <5 years)§
0.6
0.8
0.9
0.6
Hepatitis B||
1.5
1.4
0.9
0.8
0.06
0.09
Influenza
16.9
32.7
15.3
10.8
0.25
0.13
Measles
0.3
0.3
0.2
0.1
Meningococcal disease
2.3
1.5
3.6
2.5
0.12
0.08
Mumps
0.7
2.1
0.2
0.3
<0.005
<0.005
Pertussis
41.5
39.1
2.2
2.1
<0.005
0.01
Pneumococcal disease**
10.5
7.0
5.2
3.5
0.10
0.05
Rubella
0.2
0.2
0.1
<0.05
Tetanus
<0.05
<0.05
0.1
0.1
<0.005

* Data from the former period have been reported in the fourth report of this series.1 Data from the latter period are reported in this current report in the following chapters.

† Notifications where the date of diagnosis was between January 2003 and December 2007; hospitalisations where the date of separation was between July 2002 and June 2007; deaths where the death was recorded between January 2003 and December 2006.

‡ See Chapter 4 for case definitions for individual vaccine preventable disease.

§ Invasive Haemophilus influenzae type b disease for notifications. Includes Haemophilus meningitis only for hospitalisations and deaths.

|| Includes acute hepatitis B only for notifications, hospitalisations and deaths.

¶ Note the limitations of notification systems and coding for influenza hospitalisation and death data, which may grossly underestimate the true disease burden due to influenza.

** Includes pneumococcal meningitis and septicaemia only for hospitalisations and deaths.

The increasing trend of mumps notifications since 2004 continued in 2006 and especially in 2007, predominantly in adolescents and young adults, many of whom were born at a time of relatively low vaccination coverage and a single-dose schedule, and grew up during a period of reduced circulation of wild virus. While the largest numbers came from New South Wales, significant outbreaks occurred in 2007 in Indigenous communities in the Northern Territory and the Kimberley region of Western Australia.

Pertussis remains both the disease most difficult to control and for which data are most difficult to interpret. The period 2006–2007 saw lower notification and hospitalisation rates than the previous 3-year period, which included an epidemic. There was a substantial decrease in notifications among adolescents, following the commencement of school-based vaccination in 2003–2004. However, there were marked increases in notification rates in adults and hospitalisation rates in the elderly, some of which may be attributable to false positive results from serology testing, an issue detected and rectified in 2006. Strategies to reduce pertussis, especially in young infants, are being actively considered.

For almost all these diseases for which vaccination programs have been well established, disease incidence has remained low. Elimination of endogenous transmission in Australia has been achieved and maintained for some diseases, like poliomyelitis and measles, and may be nearly achieved for rubella. However, there remains an ongoing risk of importation of these diseases acquired overseas. Ongoing high vaccination coverage and effective surveillance are still required.

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Diseases with universal vaccination programs commencing in the last decade

At both national and jurisdictional levels, notification and hospitalisation rates of acute hepatitis B were stable over the 2006–2007 period, following the decline since 2001. This previously observed decline in notifications was most marked in young adults aged 15–29 years, who nevertheless remained the age group with the highest notification rates. This decline was most likely related to declining rates of intravenous drug use since 2000 and adolescent catch-up programs that commenced from the late 1990s. While a targeted program for high-risk infants began in the 1980s, the universal infant program was not implemented until 2000. The impact of this program will become more evident in the near future.

For both invasive meningococcal disease and invasive pneumococcal disease, substantial decreases in notifications, hospitalisations and deaths since implementation of the universal childhood programs with catch-up (2003 for the meningococcal program and 2005 for the pneumococcal program) were sustained with further decreases in the 2 most recent years analysed. This was predominantly due to a decrease in disease caused by the specific serogroup (meningococcal serogroup C) or serotypes (pneumococcal serotypes 4, 6B, 9V, 14, 18C, 19F, 23F) targeted by each conjugate vaccine. While the decrease in incidence of both these diseases was mainly seen in the target age groups for vaccination, herd immunity effects were also evident in other age groups not eligible for vaccination. The remaining challenges include the prevention of serogroup B meningococcal disease in infants following development of a vaccine effective against serogroup B disease, control of pneumococcal disease in older and at-risk people, and control of invasive disease caused by other serotypes, especially the emerging serotype 19A.

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Diseases with vaccination programs targeted to specific population subgroups or settings

During this reporting period, annual seasonal influenza vaccination was recommended for all Australians aged ≥65 years, all Aboriginal and Torres Strait Islander people aged ≥15 years, and all individuals aged ≥6 months who were predisposed to severe influenza or its complications, with the intention of protecting those who were more vulnerable to severe outcomes from influenza during each season. Australians aged ≥65 years, and Aboriginal and Torres Strait Islander people who were aged ≥50 years or who had chronic medical conditions that predispose them to severe influenza, were eligible for annual vaccination under the NIP. The overall as well as age-specific influenza notification rates were substantially higher in 2007 than in any previous year since national notification data became available in 2001, but hospitalisation data for the latter half of 2007 were unavailable at the time of this analysis. Although increased testing might partly explain the increase in notifications, the co-circulation of two strains of virus, A/H3N2 and A/H1N1, both of which had experienced some antigenic drift, as well as an increase in reported deaths due to influenza, including several young children, are unusual. Notwithstanding potential biases due to differences in documenting influenza notifications or hospitalisations across different age groups, it is noteworthy that the rates of notification and hospitalisation in children <5 years of age in Australia were considerably greater than in the elderly, although morbidity was predominantly in this latter age group.

Australia implemented the National Q Fever Management Program in various jurisdictions at different times during 2001 to 2006, targeting people at highest risk of occupational and environmental exposure to Q fever. While Q fever notification and hospitalisation rates declined to record low levels in 2005, no further decline occurred in 2006–2007, with the suggestion of slight increases in some jurisdictions. Multiple factors, including natural environmental factors, would have contributed. Limited availability of additional data, especially on risk factors and vaccination status, renders risk assessment and disease control difficult.

In Australia, hepatitis A generally occurs sporadically with periodic epidemic peaks related to outbreaks, although it has been endemic in the Indigenous population, especially among Indigenous children, in more remote areas. Notification and hospitalisation rates continued to decline in the 2-year review period, continuing the decline seen since the peaks in the late 1990s. Expanding from an immunisation program for Indigenous children in north Queensland, a program targeting Indigenous children aged 12–24 months in four jurisdictions (the Northern Territory, Queensland, South Australia and Western Australia) with catch-up (up to age 5 years) commenced in 2005. While this report focuses on patterns in the total population rather than Indigenous people in particular, data by jurisdiction are consistent with a substantial impact from this program.

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Diseases with recent universal vaccination programs and limited national surveillance data

For varicella, both national hospitalisation and South Australian notification data suggest an early impact of the varicella childhood immunisation program which commenced in November 2005. The impact is most marked in children aged 12–23 months, as expected, but is also seen in children aged 24–47 months. This needs to be confirmed over time and in more age groups as vaccine coverage rises. The epidemiology of herpes zoster, as reflected in the national hospitalisation data and notification data from South Australia, does not appear to have changed. Specific data on herpes zoster are limited.

For rotavirus, publicly funded vaccine for infants was available in the Northern Territory from October 2006 and nationally from July 2007. Hospitalisation data available for this report, up to June 2007, only cover the pre-vaccine period, except for a 9-month period in the Northern Territory. These showed substantial year-to-year variation. The lower notification rate for rotavirus in 2007, post vaccine introduction, observed in the Northern Territory is encouraging, but more data are required to be conclusive.

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Future surveillance priorities

While demographic data are generally complete, the completeness and consistency of some important fields in the notification records are more variable. These fields include Indigenous status, vaccination status and serogroup/subtype. National collection of additional clinical and/or laboratory data (‘enhanced’ data), as occurs currently for Hib and pneumococcal notifications, would be valuable for some other important diseases, such as pertussis and meningococcal disease, to facilitate better targeted control measures. Also, the range of diseases and information required is likely to continue to grow, with the introduction of additional vaccination programs like rotavirus and varicella in recent years and the expansion of existing programs. The use of complementary data sources, like emergency department presentations, general practice sentinel surveillance and Australian Paediatric Surveillance Unit data, for surveillance of vaccine preventable diseases should be explored. For example, linkage of the Australian Childhood Immunisation Register to morbidity and mortality data would greatly enhance the quality of vaccination status data for children as well as eliminating the resource-intensive re-collection of the information.

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Future vaccination priorities

Although the National Immunisation Program has been very effective in controlling many vaccine preventable diseases, high vaccination coverage in all the existing vaccination programs needs to be maintained. Alternative settings to primary health care for reaching specific population groups, such as school-based programs or pre-travel vaccinations, should continue to be developed. For some diseases for which higher morbidity rates are primarily due to serogroups/serotypes not contained in the available vaccine, such as meningococcal or pneumococcal disease, use of vaccines with extended coverage as they become available would be beneficial. For some other diseases (e.g. influenza, Q fever and pertussis), morbidity occurs mainly in age groups or risk groups outside those recommended for vaccination or in those too young to be vaccinated. The cost-effectiveness of expanding eligibility of existing vaccines, such as influenza for young children and boosters of pertussis vaccine for adults, will require consideration over the coming years.

Reference

1. Brotherton J, Wang H, Schaffer A, Quinn H, Menzies R, Hull B, et al. Vaccine Preventable Diseases and Vaccination Coverage in Australia, 2003 to 2005. Commun Dis Intell 2007;31(Suppl):S1–S152.

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