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Vaccine preventable diseases

This section summarises the national notification data for laboratory-confirmed influenza and invasive pneumococcal disease as well as diseases targeted by the Australian Standard Vaccination Schedule in 2001. This includes diphtheria, Haemophilus influenzae type b (Hib) infection, measles, mumps, pertussis, poliomyelitis, rubella and tetanus. The National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases (NCIRS) have recently published a detailed analysis of vaccine preventable diseases in Australia for 1999 to 2000.⁵³

Laboratory-confirmed influenza and invasive pneumococcal disease (IPD), were added to the list of nationally notifiable diseases in 2001. Both these diseases were made notifiable in all Australian states and territories during 2001. Because of the need to change public health legislation to include these diseases, complete data for 2001 were not available from all states and territories.

The rationale for the introduction of surveillance of laboratory-confirmed influenza was to give better national data on the annual incidence of influenza, the circulating viral subtypes and the effectiveness of annual influenza vaccinations. In Australia, annual vaccination against influenza is provided free of charge to non-Indigenous Australians aged 65 years and above and to Indigenous Australians aged 50 years and above. It is also recommended for individuals who are at increased risk of influenza-related complications and those who may transmit influenza to persons at increased risk.⁵⁴

There was only one change to the Childhood Immunisation Schedule in 2001 - a program for at-risk children using the seven-valent conjugate pneumococcal vaccine was recommended and publicly funded (Table 13). The program was introduced with a focus on Indigenous children, who have some of the highest incidences of invasive pneumococcal disease in the world.⁵⁵ The conjugate vaccine has been demonstrated to have an efficacy of 94 per cent in preventing invasive pneumococcal disease in young children.²

Table 13. Vaccination schedules for seven-valent conjugate pneumococcal vaccine in Australia

Date implemented	July 2001
Serogroups in vaccine	4, 6B, 9V, 14, 18C, 19F, 23F
Target populations	All Aboriginal and Torres Strait Islander infants in a 3-dose series at 2, 4 and 6 months of age, with a booster dose of the 23-valent pneumococcal polysaccharide vaccine (23vPPV) at 18-24 months of age. Catch-up is recommended for Aboriginal children in Central Australia up to the fifth birthday and for Aboriginal and Torres Strait Islander children elsewhere up to the second birthday. All Australian children with underlying predisposing medical conditions at 2, 4 and 6 months of age with a booster dose (of 7vPCV) at 12 months of age and a booster dose of 23vPPV at 4-5 years of age. Catch-up vaccination is recommended for these children up to the fifth birthday. Non-Indigenous children residing in Central Australia up to the second birthday, as catch up vaccination.
Data source	Australian Immunisation Handbook, 8th edition

There were 13,030 notifications of vaccine preventable diseases in 2001; one in eight of the total notifications to NNDSS. Pertussis was by far the most common with 9,515 notifications, or 73 per cent of all vaccine preventable disease notifications.

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Diphtheria

A single case of cutaneous diphtheria in a 52-year-old man was reported from the Northern Territory in March 2001. A toxigenic strain of Corynebacterium diphtheriae var. mitis was isolated. The patient acquired the disease in East Timor and had an uncertain vaccination history. This is the first case reported in Australia since 1993.

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Haemophilus influenzae type b disease

Notifications of Hib disease have fallen more than 30-fold since 1991, due to the efficacy of Hib conjugate vaccines (Figure 36). There were 26 notifications of Hib disease in 2001, a rate of 0.1 cases per 100,000 population. This is eight per cent less than in 2000, and the lowest number of notifications recorded since national surveillance began in 1991. Most notified cases (14, 53%) were aged less than five years and five were infants aged less than one year. Rates according to age group and sex are shown in Figure 37. There were less notifications of Hib disease for males than for females (male:female ratio 0.7:1) in 2001.

Figure 36. Trends in notifications of Haemophilus influenzae type b infections, Australia, 1991 to 2001, by month of onset



Figure 37. Notification rates of Haemophilus influenzae type b infection, Australia, 2001, by age group and sex



The Northern Territory had the highest notification rate (n=3, 1.5 cases per 100,000 population) although most cases were from New South Wales (9/26). The vaccination status of eleven cases was known; seven were unvaccinated, two partially vaccinated and two cases in Victoria were fully vaccinated. These two children were confirmed cases with documented evidence of receipt of four doses of Hib vaccine and had no identified risk factors.

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Laboratory-confirmed influenza

There were 1,286 reports of laboratory-confirmed influenza in 2001 to the NNDSS, a rate of 6.6 cases per 100,000 population. As noted above, data were not available from all states and territories for the full year, consequently these numbers are an underestimate of the true incidence. No notifications were received from Tasmania. Notifications of laboratory-confirmed influenza showed a peak in August and September (late winter). These data, together with the month when reporting began in each state or territory, are shown in Figure 38.

Figure 38. Notifications of laboratory-confirmed influenza and month when reporting to the National Notifiable Diseases Surveillance System began in each state or territory, Australia, 2001



The highest rates of laboratory-confirmed influenza were in children aged less than five years (Figure 39). The male to female ratio was 1.1:1.

Figure 39. Notification rates of laboratory-confirmed influenza, Australia, 2001, by age group and sex



In 2001, influenza A was the dominant type, 81 per cent of which were subtype H1N1 and 19 per cent were subtype H3N2. The influenza A (H1N1) isolates analysed were all A/New Caledonia/20/99-like strains. The H3N2 isolates were antigenically similar to the reference strain (A/Moscow/10/99) and the vaccine strain (A/Panama/2007/99). The influenza B isolates, which made up only 10 per cent of all (influenza A and B) isolates, were mainly B/Sichuan/379/99-like strains. Ten per cent of the influenza B isolates though were more closely related to B/Harbin/7/94-like viruses, which have circulated in previous years. The Australian 2001 influenza vaccine therefore represented a good match for the circulating viruses and 77 per cent of the over 65 year age group in Australia was vaccinated in 2001.⁵⁶

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Measles

Measles is the most important cause of vaccine-preventable death in the world. In 1998 an estimated 30 million measles cases and 880,000 measles-associated deaths occurred worldwide, with 85 per cent of deaths occurring in Africa and South-East Asia.⁵⁷ In recent years a dramatic reduction in measles incidence and elimination of endemic measles transmission has been achieved in a number of countries with a variety of vaccination strategies.⁵⁸

In Australia there were 141 measles notifications in 2001, a national rate of 0.7 cases per 100,000 population. This is a slight increase on the 107 cases reported in 2000, which was the lowest annual rate for Australia since national surveillance began in 1991 (Figure 40). The highest rate was in Victoria with 1.7 cases per 100,000 population (n=83).

Figure 40. Trends in notification rates of measles, Australia, 1991 to 2001, by month of onset



As in recent years, the age-specific notification rate of measles was highest for the 0-4 year age group (2.2 cases per 100,000 population). The rate for this age group was considerably lower than it has been in the past (Figure 41). Within the 0-4 year age group most cases (54%) were aged less than one year old. The rate for the 5-9 year age group (0.5 cases per 100,000 population) was also the lowest on record. Following the 0-4 year age group, the next highest rates were in the 20-24 year age group (2.2 cases per 100,000 population) and the 25-29 year age group (2.1 cases per 100,000 population). The proportion of cases in the 20-29 year age group has been increasing since national surveillance began, from 6 per cent in the early 1990s to above 30 per cent in 1999 to 2000. In 2001, the 20-29 year age range accounted for 41 per cent (58/141) of the reported cases.

Figure 41. Notification rates of measles, Australia, 1998 to 2001, by age group



There were a number of measles outbreaks in Australia in 2001. In January, a young Australian recently returned from India was the index case in an outbreak affecting 50 young adults in Melbourne. All cases were laboratory confirmed.⁵⁹ The median age was 25 years (range 10 months to 34 years) with 90 per cent aged 15 to 34 years. Most cases were unvaccinated and four were partially vaccinated against measles. Twenty-two (43%) of the confirmed cases were hospitalised for an average of four days (range 1-10 days) but there were no deaths.

A second outbreak of measles in Victoria was reported in October. The index case had acquired the infection overseas and there were 17 laboratory-confirmed cases linked to the index case. All 18 cases were infected with the D5 measles genotype. The majority of cases were aged between 18 and 34 years and none had a documented history of measles vaccination.

The third cluster of seven cases (five of which were laboratory confirmed) occurred in the second quarter of the year in western Sydney. The index case was probably infected while travelling overseas. Three infants aged 8-12 months and four young adults aged 19-26 years were involved in this outbreak. A measles outbreak in PNG in June 2001 prompted CDNA to warn intending travellers to that country that they should be vaccinated against measles.

In 2001, the Victorian Infectious Diseases Reference Laboratory established the National Measles Laboratory in Melbourne. The laboratory analysed samples from five Australian states and territories during the year, and 18 distinct measles strains belonging to eight different measles genotypes were identified. These observations suggest that indigenous measles transmission has been eliminated in Australia, and that periodic introductions of the virus occurs predominantly from South-East Asia.⁶⁰

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Mumps

In 2001, there were 114 notifications of mumps, a rate of 0.6 cases per 100,000 population. This is a decrease of 47 per cent on the 212 cases reported in 2000 and the lowest rate since all states and territories began notifying the disease in 1996 (although mumps was not notifiable in Queensland between July 1999 and December 2000). There were cases in most age groups (Figure 42) but the majority (n=77, 68%) were from people aged 15 years or more. Although rates were also considerably less than in 2000, the 20-24 year age group still had the highest rate of notifications (1.2 cases per 100,000 population). The next highest rates were in the 0-4 and 5-9 year age groups (both 1.1 cases per 100,000 population). Unlike most previous years, there was a slight preponderance of mumps cases in females (male:female ratio 0.8:1).

Figure 42. Notification rates of mumps, Australia, 2001, by age group and sex



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Pertussis

Pertussis continues to be the most common vaccine preventable illness in Australia, with periodic epidemics occurring at intervals of 3 to 5 years (Figure 43).⁶¹ There were 9,515 notified cases of pertussis in 2001, 60 per cent more than the 5,942 cases reported in 2000. The annual notification rate was 48.8 cases per 100,000 population.

Figure 43. Trends in notifications of pertussis, Australia, 1991 to 2001, by month of onset



Since 1999, the 10-14 year age group have had the highest notification rates of pertussis and this pattern continued in 2001 (187 cases per 100,000 population) (Figure 44). Changes in the age distribution of cases is a result of the introduction of a fifth dose of pertussis vaccine in 1994, which is given at four years of age. Children less than one year of age (particularly those under six months who have received fewer than three doses of vaccine) also have high notification rates. This age group has significantly higher morbidity and mortality than any other age group.⁵³

Figure 44. Notification rates of pertussis, Australia, 1996 to 2001, by age group



For all age groups up to 80 years there were higher notification rates in females than in males (Figure 45), and the overall male to female ratio was 0.8:1.

Top of pageFigure 45. Notification rates of pertussis, Australia, 2001, by age group and sex



Notification rates of pertussis varied considerably by geographic location (Map 6). At the state or territory level, rates were highest in South Australia (132.7 cases per 100,000 population) and lowest in Western Australia (11.9 cases per 100,000 population).

Map 6. Notification rates of pertussis, Australia, 2001, by Statistical Division of residence



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Invasive pneumococcal disease

There were 1,681 notifications of IPD in Australia in 2001, giving a rate of 8.6 cases per 100,000 population. The rates for 2001 are likely to be an under-estimate because for some jurisdictions data on IPD was not available for the whole year. While the largest number of cases were found in New South Wales, Queensland and Victoria, the highest rate occurred in the Northern Territory (48.5 cases per 100,000 population), which was more than five times the national rate. The geographical distribution of IPD varied within states and territories (Map 7), with the highest rates in central and northern Australia.

Map 7. Notification rates of invasive pneumococcal disease, Australia, 2001, by Statistical Division of residence



IPD is largely a disease of the very young and very old. In 2001 the highest rates of disease were in children aged less than five years (47.3 cases per 100,000 population) and adults aged more than 85 years (38.7 cases per 100,000 population). Rates according to age group and sex are shown in Figure 46. There were more cases among males, with a male to female ratio of 1.2:1. A peak of IPD occurred in late winter and early spring, with the largest number, 259 notifications, being reported in August 2001.

Figure 46. Notification rates of invasive pneumococcal disease, Australia, 2001, by age group and sex



Additional data were collected on cases of invasive pneumococcal disease in some Australian states and territories during 2001. Analyses of these data have recently been published.^62,63

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Poliomyelitis

No cases of poliomyelitis were reported in Australia in 2001. The National Poliovirus Reference Laboratory at the Victorian Infectious Diseases Reference Laboratory is responsible for poliovirus testing for Australia. It is also the regional reference laboratory for the Western Pacific Region (WPR) of WHO. Surveillance for acute flaccid paralysis, a clinical manifestation of poliomyelitis, is coordinated at the Victorian Infectious Diseases Reference Laboratory in collaboration with the Australian Paediatric Surveillance Unit.

There were 60 unique notifications of acute flaccid paralysis in 2001, of which 44 were classified by the Polio Expert Committee as eligible non-polio acute flaccid paralysis cases (isolates from patients resident in Australia and aged less than 15 years). Polioviruses were isolated from only one acute flaccid paralysis patient and characterised as Sabin oral poliovirus vaccine-like serotypes 1,2 and 3. In the same patient Clostridium botulinum type b organism and toxin were also detected and the case was classified as infant botulism.

As part of the laboratory containment of poliovirus, during 2001 the National Polio Reference Laboratory received viral isolates or samples stored in laboratories across Australia that may contain poliovirus. Forty Sabin-like viruses and five non-Sabin-like polioviruses were identified from 74 referred laboratory isolates and specimens.

The WPR, of which Australia is a member nation, was declared free of circulating wild poliovirus in October 2000. During 2001, however, viruses derived from the Sabin oral polio vaccine caused three cases of poliomyelitis in the Philippines, also a member nation of the WPR. The identification of these three cases has emphasised the necessity of maintaining a high level of vaccination coverage within Australia and an effective surveillance system to detect cases of poliomyelitis.⁶⁴

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Rubella

Since 1995 the annual number of rubella notifications have been declining. This decrease has occurred at the same time as the measles, mumps and rubella vaccination coverage rates have increased. In 2001, there were 263 notifications, a notification rate of 1.3 cases per 100,000 population, an 18 per cent decrease from the 322 cases of rubella reported in 2000. This is the lowest rate on record since the NNDSS commenced in 1991. As in previous years, the highest number of notified cases occurred in October, reflecting the usual seasonal increase in spring months. The highest notification rate was in Queensland (3.7 cases per 100,000 population).

In 2001, notification rates were highest in males in the 20-24 year age group (11.3 cases per 100,000 population, Figure 47). As in previous years, there were more males than females notified with rubella (male:female ratio 2.5:1) and the ratio is higher than in the past five years.

Figure 47. Notification rates of rubella, Australia, 2001, by age group and sex



There were 49 cases of rubella in women of childbearing age (15-49 years) in 2001. Seven cases occurred in young infants, five within two months of birth. There were no notifications of congenital rubella in 2001.

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Tetanus

There have been less than eight cases of tetanus notified each year in Australia since 1995 mainly in adults aged over 70 years. In 2001, there were three cases. Two were aged 70 years or more and the third was also an adult. Two cases were male and one cases was female.

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Childhood vaccination coverage reports

Estimates of vaccination coverage both overall and for individual vaccines for children at 12 months of age continued to improve in 2001. This trend was also evident in each state and territory. Vaccination coverage at one year of age is shown in Table 14.

Table 14. Percentage of Australian children born in 2000 vaccinated according to data available on the Australian Childhood Immunisation Register. Estimate at one year of age

Vaccine group	Per cent vaccinated
	1 Jan-31 Mar 2000	1 Apr-30 Jun 2000	1 Jul-30 Sep 2000	1 Oct-31 Dec 2000
DTP	91.8	91.9	92.2	92.0
OPV	91.7	91.8	92.1	91.9
Hib	94.8	94.5	94.3	94.5
Hepatitis B	NA	NA	94.3	94.4
Fully vaccinated	91.5	91.2	90.4	90.5

DTP Diphtheria-tetanus-pertussis
OPV Oral polio vaccine
NA Not available

Vaccination coverage at two years of age was first reported in 1998. Coverage estimates for vaccines recommended at 12 and 18 months of age were higher in 2001, compared with the previous year, as were the estimates for being 'fully vaccinated' at two years of age. Vaccination coverage at two years of age is shown in Table 15. The reported 'fully vaccinated' coverage levels are lower than the levels for individual vaccines, because children who have missed vaccination against some diseases are not necessarily those who have missed vaccination against the other diseases. It is important to note that in other countries such as the United Kingdom, three doses of the diphtheria-tetanus-pertussis and Hib vaccines constitute full vaccination for these vaccines at two years of age.

Table 15. Percentage of Australian children born in 1999 vaccinated according to data available on the Australian Childhood Immunisation Register. Estimate at two years of age

Vaccine group	Per cent vaccinated
	1 Jan-31 Mar 1999	1 Apr-30 Jun 1999	1 Jul-30 Sep 1999	1 Oct-31 Dec 1999
DTP	89.5	89.8	90.3	90.2
OPV	93.9	93.9	94.3	94.4
Hib	95.0	95.2	95.3	95.4
MMR	92.8	93.1	93.2	93.4
Fully vaccinated	86.6	87.0	88.0	87.8

DTP Diphtheria-tetanus-pertussis.
OPV Oral polio vaccine.
MMR Measles-mumps-rubella.

This article was published in Communicable Diseases Intelligence Volume 27, No 1, March 2003.