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Vaccine preventable diseases

Introduction

This section summarises the national notification data for diseases targeted by the Australian Standard Childhood Vaccination Schedule in 2000. This includes diphtheria, Haemophilus influenzae type b infection, measles, mumps, pertussis, poliomyelitis, rubella and tetanus.

There were 6,617 notifications of vaccine preventable diseases (VPDs) in 2000; 7.4 per cent of the total notifications. Pertussis was by far the most common accounting for 5,942 notifications or 89.8 per cent of all VPD notifications. Notifications of vaccine preventable diseases to the NNDSS and notification rates for vaccine preventable diseases in Australia are shown in Tables 17 and 18.

Table 17. Trends in notifications of vaccine preventable diseases, Australia, 1991 to 2000*

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Diphtheria	1	12	0	0	0	0	0	0	0	0
Haemophilus influenzae type b	533	465	370	163	77	49	51	35	40	28
Measles	1,438	1,452	4,693	4,805	1,185	481	838	288	238	107
Mumps	-	-	-	-	156	125	191	182	172	212
Pertussis	343	795	4,413	5,441	4,230	4,545	10,825	5,791	4,417	5,942
Rubella	-	-	4,006	3,488	5,751	2,933	1,387	753	377	322
Tetanus	13	13	10	13	7	3	7	8	2	6

* All jurisdictions reported for all years with the following exceptions:
Haemophilus influenzae type b not reported from Western Australia (1991 to 1993).
Mumps not reported from Queensland (1995,1996, 1999 and 2000).
Rubella not reported from Tasmania (1993 to 1994).
Tetanus not reported from Queensland (1991 to 1993).

Table 18. Trends in notification rates of vaccine preventable diseases, Australia, 1991 to 2000* (rate per 100,000 population)

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Diphtheria	< 0.1	0.1	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Haemophilus influenzae type b	3.4	2.9	2.3	0.9	0.4	0.3	0.3	0.2	0.2	0.1
Measles	8.3	8.3	26.6	26.9	6.6	2.6	4.5	1.5	1.3	0.6
Mumps	-	-	-	-	1.1	0.8	1.0	1.0	1.1	1.4
Pertussis	2.0	4.5	25.0	30.5	23.4	24.8	58.4	30.9	23.3	31.0
Rubella	-	-	23.3	20.1	31.8	16.0	7.5	4.0	2.0	1.7
Tetanus	0.1	0.1	0.1	0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1

* All jurisdictions reported for all years with the following exceptions:
Haemophilus influenzae type b not reported from Western Australia (1991 to 1993).
Mumps not reported from Queensland (1995,1996, 1999 and 2000).
Rubella not reported from Tasmania (1993 to 1994).
Tetanus not reported from Queensland (1991 to 1993).

In 2000, the following changes to the childhood immunisation schedule²⁵ occurred:

New vaccines

New combination vaccines for:

• diphtheria-tetanus-acellular pertussis-hepatitis B (DTPa-hepB); and
• Haemophilus influenzae type b - hepatitis B (Hib (PRP-OMP)-hep B),

for all three doses in the primary vaccination schedule. This allowed the introduction of universal hepatitis B vaccination (commencing at birth) without requiring an extra injection.

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New schedule

• Two alternative schedules depending on which of the above combination vaccines is used and differing only in the timing of the 4th dose of these vaccines.
• All Australian children recommended to receive the same Hib vaccine (PRP-OMP), which reduces the number of injections and the complexity of the schedule.
• Introduction of universal vaccination for hepatitis B beginning at birth. Infants born to hepatitis B carrier mothers receive hepatitis B immunoglobulin and vaccine at birth. Preadolescent hepatitis B vaccination now recommended at 10-13 years. Booster doses of hepatitis B vaccine no longer recommended.
• Second booster of DTPa now recommended at 4 years, instead of 4-5 years.
• Second dose of MMR now given at 4 years instead of 10-16 years.
• Tetanus and diphtheria boosters no longer recommended every 10 years. A tetanus booster at age 50 is recommended if no boosters have been given within the last 10 years.
• Inactivated poliomyelitis vaccine is an acceptable alternative to live, oral poliomyelitis vaccine (OPV) in the primary vaccination schedule. However, OPV will remain the publicly funded vaccine.
• Influenza vaccine recommended for children with cystic fibrosis, people with severe asthma and pregnant women in the second or third trimester of pregnancy during the influenza season.

The annual report of vaccination coverage estimates for children aged 12 months and the second annual report for children aged 24 months (using data extracted from the Australian Childhood Immunisation Register-ACIR) are also included in this section. A full description of the methodology used for calculating these estimates have been described previously.⁴²

Diphtheria

There were no cases of diphtheria notified in 2000. The last known case occurred in 1992 and was notified in 1993. There has been a dramatic decline in the incidence of diphtheria in Australia since the first half of the 20th century (Figure 27).

Figure 27. Trends in notifications of diphtheria, Australia, 1917 to 1998



At the height of the 1921 diphtheria outbreak in Australia, there were 23,199 notifications giving a notification rate of 426 cases per 100,000 population.⁴³ Although diphtheria hasn't been found in Australia since 1992, a recent case in New Zealand⁴⁴ and the extensive outbreak in the former states of the Soviet Union in the 1990s⁴⁵ highlight the potential for diphtheria to re-emerge.

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Haemophilus influenzae type b disease

Notifications of Haemophilus influenzae type b (Hib) have fallen more than 30-fold since 1991 due to the impact of Hib conjugate vaccines (Figure 28). An assessment of the impact of conjugate vaccines on the global incidence of Hib disease concluded that few vaccines have induced such dramatic declines in disease incidence in such a short time. The prevention of nasopharyngeal colonisation by Hib in vaccinated individuals under most circumstances may explain the dramatic impact on Hib disease.⁴⁶

Figure 28. Trends in notifications of Haemophilus influenzae type b infection, Australia, 1991 to 2000



There were 28 notifications of Hib disease in 2000, a rate of 0.1 cases per 100,000 population. This is 30 per cent less than in 1999, and the lowest number of notifications recorded since national surveillance began in 1991. As in previous years most notified cases (10, 36%) were less than 5 years of age. However the number and proportion of all cases in this age group has been declining. The most dramatic decreases have been in those aged less than two years. Infants aged less than 1 year, however, continued to have the highest rate in 2000 (2.4 cases per 100,000 population) (Figure 29). There were more males than females (male:female ratio 1.8:1) notified with Hib disease in 2000.

Figure 29. Notification rates of Haemophilus influenzae type b infection, Australia, 2000, by age and sex



The Northern Territory had the highest notification rate (1 case per 100,000 population, 2 cases) although most cases (12/28) were from Queensland. Two cases occurred in fully vaccinated individuals, seven in partially vaccinated and five in unvaccinated individuals. The vaccination status for the other 14 cases was unknown.

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Measles

Measles is the most important cause of vaccine preventable death in the world. In 1998, there were an estimated 30 million measles cases and 880,000 measles-associated deaths worldwide with 85 per cent of deaths occurring in Africa and South East Asia.⁴⁷ In recent years there has been a dramatic reduction in measles incidence and endemic measles transmission has been eliminated in a number of countries using a variety of vaccination strategies.⁴⁸

In Australia, measles reports to the NNDSS are at the lowest levels ever recorded (Figure 30). This is the result of a series of successful vaccination initiatives over the past few years. One such initiative was the Australian Measles Control Campaign (August to November 1998) which involved vaccinating 1.7 million primary school children with the Measles-Mumps-Rubella vaccine (MMR) regardless of their past vaccination history. As a result, immunity to measles among these children increased from 84 per cent to 94 per cent.⁴⁹

Figure 30. Trends in notification rates of measles, Australia, 1991 to 2000, by month of onset



There is evidence that endemic transmission of measles in some parts of Australia is being interrupted. All measles cases in Western Australia in 1999/2000 were imported from overseas or epidemiologically linked to imported cases. (Dowse, Communicable Diseases Control Conference, April 2001, Abstract 58). Using measles virus genotyping, Lambert and colleagues have shown that endemic measles virus strains are no longer circulating in Victoria. Instead, sporadic introduction of imported strains is responsible for limited focal spread. (Lambert, Communicable Diseases Conference, April 2001, Abstract 60). If one accepts that measles elimination should be defined as a situation in which endemic transmission has stopped, sustained transmission cannot occur (because the proportion of susceptible people is sufficiently low), and secondary spread from importations will end naturally without intervention,⁵⁰ then Australia may have already achieved measles elimination.

There were 107 cases of measles notified in 2000, a national rate of 0.6 cases per 100,000 population. This is less than half the number reported in 1999 and is the lowest annual rate for Australia since national surveillance began in 1991. In 2000, Western Australia and the Australian Capital Territory began laboratory testing of all notified cases and initiated improved contact tracing. The highest rates of notification were in the Australian Capital Territory (1 case per 100,000 population; 3 cases), Queensland (0.7 cases per 100,000 population; 26 cases) and South Australia (0.7 cases per 100,000 population; 11 cases) (Tables 2 and 3). Twenty-two cases were documented as acquired overseas and 21 cases resulted from seven identified outbreaks in which the index case had acquired measles outside Australia. The source of infection for the remaining 85 cases was not recorded.

As in recent years, age-specific notification rates were highest for the 0-4 year age group (2.5 cases per 100,000 population) especially those aged less than one year (3.6 cases per 100,000 population) and one year of age (5.2 cases per 100,000 population). Rates for this age group were, however, considerably lower than in the past (Figure 31). Rates for the 5-9 year age group (0.8 cases per 100,000 population) were also the lowest on record.

Figure 31. Trends in notification rates of measles, Australia, 1998 to 2000, by age group



The 20-24 year age group had the second highest age-specific rate (1.7 cases per 100,000 population) and accounted for 21 per cent (23/107) of the reported cases in 2000 (similar to the 20% of cases this age group contributed in 1999). This age group is a 'missed middle' of young adults born in the second half of the 1970s, who have neither been vaccinated nor exposed to the wild measles virus. In the past few years, Australia has recorded measles outbreaks among young adults, often associated with an index case who has travelled to countries with high endemic levels of measles.^51,52,53 As in past years there were similar numbers of males and females with measles reported in 2000 (male:female ratio 1.1:1, Figure 32).

Top of pageFigure 32. Notification rates of measles, Australia, 2000, by age and sex

Mumps

Mumps notification rates in Australia have been close to 1.0 cases per 100,000 population since 1997 (Table 18). Increased coverage of the Australian population with the MMR vaccine has not had the dramatic impact on mumps incidence that has been seen for measles and rubella. Moreover, in recent years the notification rates for mumps have increased in older age groups, in whom mumps morbidity is more severe (Figure 33). Increased use of the MMR vaccine in adolescents and adults over the next few years and ongoing surveillance are essential for mumps control and elimination in Australia. (Gidding, Communicable Diseases Control Conference, April 2001, Abstract 57)

Figure 33. Trends in notification rates of mumps, Australia, 1993 to 2000, by age group



In 2000, there were 212 notifications of mumps, a rate of 1.4 cases per 100,000 population. This is above the WHO elimination target of <1 case per 100,000 population and is a 23% increase on the 172 cases reported in 1999. There were cases in most age groups with the majority (151, 71%) aged 15 years or more (Figure 34). In contrast with previous years the highest notification rates were in the 20-24 year age group (3.1 cases per 100,000 population) and the 15-19 year age group (2.6 cases per 100,000 population). This pattern was apparent even in New South Wales where only laboratory-confirmed cases are notifiable. Overall, there was a slight preponderance of mumps notifications from males (male:female ratio 1.3:1). Mumps was not notifiable in Queensland from July 1999 to December 2000.

Figure 34. Notification rates of mumps, Australia, 2000, by age 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 35).⁵⁴ As a result of infant immunisation against pertussis in Australia (five doses given at 2, 4, 6, 18 and 48 months) the peak notification rate is now found among young adolescents (aged 10-14)(Figure 36).

Figure 35. Trends in notification rates of pertussis, Australia, 1991 to 2000, by month of onset



Figure 36. Trends in notification rates of pertussis, Australia, 1996 to 2000, by age group



Despite high levels of vaccination, pertussis has increased in a number of countries since 1997. This has prompted investigations into the evolution of variants of Bordetella pertussis. Mooi and colleagues have observed antigenic divergence between vaccine strains and clinical isolates of Bordetella pertussis specifically in the surface-associated protein pertactin and the pertussis toxin.⁵⁵ Replacement of vaccine with non-vaccine strains as a result of herd immunity has not yet had any measurable effect on pertussis vaccine efficacy, but surveillance of variant strains of the bacteria may be important for the control of pertussis in the future.

Several recent studies have examined the importance of pertussis as a cause of prolonged coughing in adults and adolescents. A recent study in Canada suggests that up to 20 per cent of prolonged coughs are associated with laboratory evidence of pertussis infection.⁵⁶ The nature of that evidence is controversial, however, as only 2.3 per cent of symptomatic cases were confirmed by culture, PCR or a fourfold increase in pertussis antibody. The remainder were diagnosed on the basis of a single high pertussis antibody titre.

Since it is well established that adolescents and adults are frequently the source of pertussis infection for infants and children, and adolescents now have the highest rates of disease, vaccination of adolescents with acellular pertussis vaccines has been instituted in France, Germany and Canada. It remains to be seen how this will impact on the epidemiology of pertussis in these countries. Implementation of an adolescent vaccination program in Australia is currently being considered by a working party of the Australian Technical Advisory Group on Immunisation (ATAGI).

There were 5,942 notified cases of pertussis in 2000, 1,525 more than in 1999. The annual notification rate was 31.0 cases per 100,000 population. Pertussis notifications peaked in August, when 721 cases were notified. As in 1999, the 10-14 year age group had the highest notification rate of pertussis (117.7 cases per 100,000 population) (Figure 37).

Top of pageFigure 37. Notification rates of pertussis, Australia, 2000, by age and sex



Notification rates of pertussis varied considerably by geographic location (Map 6). At the State/Territory level, rates were highest in the Australian Capital Territory (66.2 cases per 100,000 population) and lowest in the Northern Territory (2.6 cases per 100,000 population), where only 5 cases were notified. In 2000, South Australia included pertussis cases diagnosed by PCR for the first time.

Map 6. Notification rates of pertussis, Australia, 2000, by Statistical Division of residence

Poliomyelitis

No cases of poliomyelitis were reported in Australia in 2000. It is difficult to determine exactly when the last case of locally acquired poliomyelitis occurred in Australia. However, the last laboratory confirmed case was in 1967 and there were three clinically compatible cases notified in 1972 with no additional information currently available.⁵⁷ All cases notified since 1972 have been investigated further and this has led them to be re-classified as cases of vaccine-associated poliomyelitis. The last known imported case of poliomyelitis was due to wild poliovirus type 1 in 1977.

On 29 October 2000, the WHO certified the Western Pacific Region polio-free.⁵⁸ The last recorded case in the region was reported in Cambodia in 1997.

Since the live oral polio vaccine has the potential to cause vaccine associated disease, the USA has recently replaced this vaccine with an inactivated polio vaccine. This issue is under consideration in Australia by ATAGI

A report on the Australian National Polio Reference Laboratory is given later in this report (p188).

Rubella

Since 1995, annual numbers of rubella notifications have been declining (Figure 38). This decrease has occurred at the same time as MMR vaccine usage has been increasing. In 2000, there were 322 notifications, a notification rate of 1.7 cases per 100,000 population. This is the lowest on record both nationally and in each State or Territory. As in previous years, the highest number of notified cases occurred in October, reflecting the expected seasonal increase in Spring months. The highest notification rate was from New South Wales (3.0 cases per 100,000 population), where all cases were laboratory-confirmed.

Figure 38. Trends in notification rates of rubella, Australia, 1991 to 2000, by month of onset



In 2000, the notification rate of rubella was highest in males in the 20-24 year age group (11.2 cases per 100,000 population, Figure 39). However, rates for this group have been decreasing in recent years due to the replacement of the schoolgirl rubella program with adolescent vaccination of both males and females between 1994 and 1998. Overall, there were more males than females notified with rubella (male:female ratio 2.0:1) in 2000.

Top of pageFigure 39. Notification rates of rubella, Australia, 2000, by age and sex



There were 68 notifications of rubella from women of childbearing age (15-49 years) in 2000, a rate of 1.4 cases per 100,000 population. No notifications of congenital rubella were received in 2000. (Annual Report of the Australian Paediatric Surveillance Unit). Only 6 cases of congenital rubella have been reported since 1995, with the last case notified in 1999.

Tetanus

In 2000, there were 6 cases of tetanus notified to the NNDSS. Five of these were in adults aged 50 years or greater and one was in an infant. Of the 6 cases, 1 was partially vaccinated, 2 were unvaccinated (including the 2-year-old infant) and the vaccination status of the other three was unknown. Five of the 6 cases were females.

Childhood vaccination coverage reports

Estimates of vaccination coverage for both 'fully vaccinated' and individual vaccines for children at 12 months of age continued to improve in 2000 (Table 19). This trend was also evident in each State and Territory. Vaccination coverage at 12 months of age for Australia as a whole has now surpassed the Immunise Australia Program target of 90 per cent coverage for the first milestone vaccines.

Table 19. Percentage of Australian children born in 1999 vaccinated at one year of age for four consecutive birth cohorts assessed during 2000 using the Australian Childhood Immunisation Register

Vaccine group	% vaccinated
	1 Jan to 31 Mar 1999	1 Apr to 30 Jun 1999	1 Jul to 30 Sep 1999	1 Oct to 31 Dec 1999
DTP	89.8	89.8	91.8	91.5
OPV	89.8	90.2	91.8	91.4
Hib	89.3	90.3	91.7	94.6
Fully vaccinated	88.4	89.0	91.3	91.2

Vaccination coverage at 2 years of age was first reported in 1998. Coverage estimates for individual vaccines recommended at 12 months and 18 months of age were higher in 2000 compared with the previous year, as were the estimates for being 'fully vaccinated' at 2 years of age (Table 20). 'Fully vaccinated' coverage estimates were reported to be considerably lower than estimates for individual vaccines. One likely factor is poor identification of children on immunisation encounter forms, which leads to difficulties matching new and existing vaccination records on the ACIR. Further, in their regular parent surveys, the Health Insurance Commission have found some parents have an objection to particular vaccines, although not always the same vaccines. It is important to note that in countries such as the United Kingdom, three doses of diphtheria-tetanus-poliomeylitis vaccine (DTP) and Hib vaccine constitute full vaccination with these vaccines at 2 years of age.

Table 20. Percentage of Australian children born in 1998 vaccinated at 2 years of age for four consecutive birth cohorts, assessed during 2000 using the Australian Childhood Immunisation Register

Vaccine group	% vaccinated
	1 Jan to 31 Mar 1998	1 Apr to 30 Jun 1998	1 Jul to 30 Sep 1998	1 Oct to 31 Dec 1998
DTP	87.5	88.9	89.6	88.3
OPV	91.9	92.2	92.7	93.1
Hib	87.2	89.2	89.6	94.7
MMR	91.0	91.3	92.3	92.4
Fully vaccinated	81.7	83.4	85.1	84.8

This article was published in Communicable Diseases Intelligence Volume 26, No 2, June 2002