Poliomyelitis, tetanus, diphtheria, pertussis, measles, rubella, mumps, invasive Haemophilus influenzae type b disease
Poliomyelitis, tetanus and diphtheria
Australia and the Western Pacific region have been declared polio free, but the overseas acquired case in 2007 highlights the ongoing need for high vaccination coverage and improved active surveillance for acute flaccid paralysis until global eradication 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. Tetanus continues to occur at a very low but declining rate with an average of 3 cases per year in 2006–2007 compared with 4 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 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 among travellers.
Pertussis remains a disease that is difficult to control and whose data are difficult to interpret. The period 2006–2007 saw lower notification and hospitalisation rates than the previous 3-year period which included an epidemic. Notification rates decreased in children and adolescents, with the greatest decrease seen in 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. It remains unclear how much of these increases was due to false positive results from serology testing, an issue that was detected and rectified in 2006. There are limited data on morbidity and mortality from pertussis in older persons internationally, but the continuing high notification and hospitalisation rates, as well as 2 deaths, seen in Australia suggests that immunisation against pertussis as well as tetanus is an important consideration in persons >60 years of age. Currently immunisation is only recommended in the context of potential contact with young infants.3
Measles and rubella
During 2006–2007, measles and rubella notifications and hospitalisations continued at very low levels, similar to those in the previous 2–3 year period. A relatively large number of cases were reported in 2006 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. This is still consistent with the elimination of endemic transmission in Australia as these outbreaks were not sustained. Unlike in previous reports, young adults did not have the highest notification rate during this study period. However, more data are required before their continued status as a susceptible age group can be ruled out. The maintenance of high 2-dose vaccine coverage in pre-school children remains the cornerstone of measles control, but increased emphasis on travel vaccination and monitoring of imported cases may require more attention in the future. 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, and Indigenous women in some communities, have been identified as having lower immunity and being therefore at higher risk of infection in pregnancy. The laboratory identification and typing of measles isolates is now a critical component of surveillance to demonstrate the absence of circulating endemic strains. This is likely to be required for rubella in the future when the goal of elimination is adopted.
A considerable increase in mumps notifications was seen 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, a single-dose schedule, and reduced circulation of wild virus. While the largest numbers came from New South Wales, outbreaks were also seen in Indigenous communities in the Northern Territory and the Kimberley region of Western Australia, where a reduced response to an earlier dose given at 9 months of age in the Northern Territory in the 1980s and 1990s appears to be a contributing factor. However, as well as reduced immunity due to these factors, a substantial minority of Indigenous and non-Indigenous cases had received 2 doses of vaccine, at 12 months of age and in adolescence. This had also been observed in the USA and the UK previously, where epidemics had peaked earlier than in Australia. This is probably attributable to lesser and less sustained antibody responses to mumps antigen compared with measles and rubella and may warrant consideration of an additional booster dose, at least in some settings.
Invasive Haemophilus influenzae type b disease
The virtual disappearance of invasive Hib disease among children aged <5 years has been an ongoing success story for vaccination with continued year-on-year falls in notifications of invasive Hib disease during 2006–2007. 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.