Measles and rubellaDuring 2003–2005, measles and rubella notifications and hospitalisations continued their decline, reaching record lows, with about 90% and 80% reductions, respectively, compared with earlier in the decade. These achievements reflect the success of the Measles Control Campaign as well as ongoing high childhood vaccination coverage with measles-mumps-rubella (MMR) vaccine. Australia’s remaining susceptible cohort of young adults born in the 1970s and early 1980s were targeted by a young adult MMR vaccination campaign in 2001. Both a serological evaluation130 and data presented in this report suggest that the campaign failed to significantly improve immunity in this age group. Improving immunity in this cohort and communicating the potentially serious nature of infection with measles and rubella in the face of near absent disease remain important and far from hypothetical challenges. Whilst regional measles elimination would appear to be in reach, regionally rubella control remains at an early stage. The laboratory identification and typing of isolates from measles and rubella cases is now vital in order to monitor the origin and any transmission of these diseases in Australia.
MumpsSince 2002, when mumps notifications were the lowest on record, mumps notifications have increased, and in 2005 reached the highest level since notification began in 1993. This rise was primarily due to increased notification rates in the 20–34 year age group, especially in Queensland and New South Wales, with the highest incidence occurring during 2005 in the 25–29 year old age group (5.1 per 100,000). Notification rates in children remained low. Despite the increase in mumps notifications, rates in Australia were low in comparison to the rates experienced in the United Kingdom during the epidemic of mumps in 2004/2005.146 The peak age group affected in the UK, and also in recent outbreaks in the USA,148 were 18–24 year olds. Thus, Australia faces similar issues to other developed countries that are also experiencing mumps resurgence in older susceptible cohorts. The high notification rates in the 20–34 year age group suggest that some endemic transmission may be occurring in this age group. Surveillance for mumps and further consideration of initiatives to effectively target young adults for immunisation are of continued importance in the Australian context.
Hib diseaseThe virtual disappearance of invasive Hib disease among children less than five years old has been an ongoing success story for vaccination with continued year on year falls in notifications of invasive Hib disease during 2003–2005. Laboratory confirmation with definitive typing remains very important, now that Hib disease is even rarer and as the relative incidence of non-type b invasive Haemophilus influenzae increases. Surveillance of Hib disease, through hospitalisation data, would greatly benefit from a specific ICD code for type b disease, which would provide an additional source of information independent from notifications.
PertussisTrends in pertussis are difficult to interpret as the disease is by nature variable with peaks every 3–4 years. It stands out as an ongoing challenge, with an epidemic year experienced in 2005 greater in size than the previous peak (>11,000 notifications compared with about 9,600 in 2001). However, it is encouraging that pertussis notifications and hospitalisations have fallen in the most immunised age group (1–10 years), with most notifications occurring either in those too young to be immunised or in adolescents and adults whose vaccine-derived or infection-induced immunity has waned over time. The review period saw the incorporation of a booster dose of pertussis vaccine in adolescence and, although it is still early, there are data to support the success of this strategy already, driven perhaps by the active catch-up adolescent programs implemented in two states. Current recommendations also encourage dTpa vaccination for prospective and recent parents and for adults working with young children, but uptake is uncertain and unlikely to be high.76
InfluenzaThe data presented in this report, although minimal estimates of influenza cases, indicate that the disease burden from influenza is large, with the highest number of hospitalisations and bed days occurring at the extremes of age, in children under five years of age and in the elderly. There are intermittent surges in influenza every few years but data from Australia and the UK are consistent with a gradual decline in such peaks; these are largely due to influenza A H3N2 that started as a pandemic strain in 1968 and to which (and its many drift variants) substantial herd immunity has developed. Influenza notifications commenced nationally in 2001 for laboratory-confirmed cases and, although a gross underestimate of disease burden, these provide useful information about the relative size of influenza seasons, circulating influenza strains and changes in age distribution consequent upon vaccination. However, caution in interpretation of these data is required due to differential rates of testing among jurisdictions and age groups. Annual influenza vaccination is currently recommended as the primary method of influenza prevention in people aged 65 years and over, all Indigenous people aged 50 years and over, and all individuals aged 6 months and over with chronic medical conditions likely to be exacerbated by influenza or its complications, e.g. chronic pulmonary or cardiovascular disease.76 Vaccination uptake in Australians aged 65 years and over was estimated at 76.9% and 79.1% for 2003110 and 2004,111 respectively. Extension of influenza vaccination to all adult Indigenous people should be considered as both influenza hospitalisation rates and mortality related to influenza and pneumonia are twice that documented in persons of non-Indigenous background across all age groups.77 As for the paediatric population, in 2003, the USA Advisory Committee on Immunization Practices (ACIP) recommended routine influenza vaccination113,114 of healthy American children aged 6–23 months based on the high burden of illness.99,115,116 More recently, in 2006, the ACIP extended its recommendation to include children up to the age of five years.117 Whilst available Australian data suggest a similar significant burden of illness in young children,118,119 examination of cost-effectiveness, efficacy and feasibility of universal immunisation of healthy children is required before implementing such a population level strategy.120 Notwithstanding bias due to variable rates of documenting notification or hospitalisation across different age groups, it is noteworthy that, during 2003–2005, notifications in children under 5 years of age were five times greater than in the elderly aged 60 years and over and hospitalisation rates were, similarly, four times higher.
Hepatitis BAt both national and jurisdictional levels, notifications increased between 1993 and 2001 and since then have declined, while hospitalisations have remained steady since 1999. Notification rates in Victoria are disproportionately high compared with other jurisdictions, probably reflecting a more active approach to surveillance. However, hospitalisation rates are also higher suggesting the possibility of a truly higher rate of disease in Victoria. The review period saw a decline in notifications that was most marked in young adults aged 15–24 years. However, it is too soon to expect such a decline as a consequence of universal neonatal vaccination, which commenced nationally in 2000. One potential reason for the considerable reduction in notifications, particularly in 15–24 year olds, is the declining rates of intravenous drug use since 2000, consistent with trends in hepatitis C virus notifications.90 It is likely that the impact of both the targeted infant and catch-up adolescent vaccination programs will become more evident in the next 5–10 years.
Rare vaccine preventable diseases (tetanus, diphtheria and poliomyelitis)Tetanus continues to occur at a very low but seemingly declining rate with an average of five cases per year in 2000–2002 compared with 3.7 cases per year in 2003–2005. Tetanus is now largely a disease of older adults, reinforcing the need to check tetanus vaccination status when older adults present for other reasons, such as a routine visit for annual influenza vaccination. There is an ongoing risk of the importation of diphtheria into Australia from regions where diphtheria is not well controlled, reinforcing the need for ensuring adequate immunisation across all age groups, especially amongst travellers. Australia and the Western Pacific region have been declared polio free,303 but the importation and subsequent polio outbreak in Indonesia in 2005185 highlight the ongoing need for high vaccination coverage and improved active surveillance for acute flaccid paralysis until global certification is achieved. The routine use of IPV, implemented in late 2005, will eliminate the small risk of vaccine-associated paralytic poliomyelitis. With the replacement of OPV with IPV in Australia, incidental detection of polioviruses in faecal specimens should no longer occur. Future poliovirus isolations will, therefore, require full investigation.179
Varicella-zosterWith the introduction of varicella-zoster vaccine in late 2005, surveillance of the disease burden due to both varicella and zoster have become greater priorities. Because disease modelling has raised the possibility that an increase in zoster disease may flow on from a reduction in varicella (through reduction of natural ‘boosting’ of immunity due to intermittent exposure to varicella infection in the community),287 zoster surveillance will be as important as documenting declines in varicella infection in the coming years. Currently, surveillance data from the USA, where varicella immunisation has been recommended for over a decade, indicates a large reduction in varicella morbidity with no increase in zoster disease yet demonstrated.291 The availability of a vaccine to prevent zoster may become an important option in the future should surveillance detect an increase in zoster disease.283
Varicella-zoster surveillance has been funded as part of the national varicella immunisation program292 and will include notification to the NNDSS (in five jurisdictions, surveillance will comprise passive notification through GPs and labs; in two, it will include passive notification as well as syndromic surveillance, with specimen collection through sentinel GPs/emergency departments; and in one state, varicella will not be notifiable, with emergency department syndromic surveillance only).293 Additionally trends in disease burden will continue to be reviewed through hospitalisation data and Australian Paediatric Surveillance Unit data on neonatal and congenital varicella infections as well as severe infections in older children requiring hospitalisation.
Pneumococcal diseaseVaccination with the 23vPPV has been funded nationally since 1999 for Aboriginal and Torres Strait Islander adults aged 50 years and over, and those aged 15–49 years with high-risk conditions.3 Nationally funded 7vPCV vaccination commenced in 2001 for all Aboriginal and Torres Strait Islander infants and other infants with high-risk conditions.3 In 2005, the 7vPCV was funded for all Australian infants and the 23vPPV for all aged 65 years and over. Data in this report suggest a noticeable impact in the first year of universal infant vaccination as, in 2005, the IPD notification rate declined by 25% overall and by 66% in those aged less than two years compared to the three previous years, and by 80% in cases with serotypes contained in the vaccine. Smaller decreases occurred in all other age groups, but these should be interpreted with caution due to the smaller numbers of cases in these age groups. Hospitalisation rates were lower in 2004/2005 compared to previous years, although this included only the first six months of the funded vaccination program. There were decreases in all age groups, but the greatest decrease was seen in infants (37%).
Concerns about replacement disease by serotypes not contained in the vaccine have been expressed.167 In the US, some replacement IPD appears to have occurred, but there is still a substantial overall decrease in IPD notifications.164 The data presented here for Australia on the first year of the vaccination program suggest the possibility of some replacement disease in unvaccinated age groups, but a substantial overall decline in IPD rates. It will be important to monitor this closely in future.
Disparities between Indigenous and non-Indigenous children may re-emerge following universal vaccination, due to higher rates of non-vaccine type disease in Indigenous people.163 New conjugate vaccines with greater serotype coverage may be necessary to address this and the persistent high rates in Northern Territory Indigenous adults.
Meningococcal diseaseThe incidence of meningococcal disease in Australia increased continuously between 1991 and 2002.3 Following the introduction of the routine and catch-up meningococcal C vaccination programs in January 2003 for those born after 1983 (aged 19 years in 2003),136 there has been a marked decrease in meningococcal disease notifications, hospitalisations and deaths. The reduction in notifications occurred for both serogroup C disease and those where serogroup information was not available, while notifications for serogroup B and other serogroups, mainly W135 and Y, remained relatively stable. A challenge remains to control serogroup C disease in young adults in whom the catch-up campaign was less comprehensive than for those immunised in schools.
The high burden of meningococcal disease in infants, particularly non-vaccine preventable serogroup B disease, emphasises the importance of early recognition and appropriate clinical management of disease and the need for a vaccine to reduce the significant morbidity and mortality. Several candidate serogroup B vaccines are under investigation in international Phase II clinical trials.142 However, availability of a universal serogroup B vaccine appropriate for use in Australia is still some way off.