An early impact of the national varicella immunisation program appears to be evident in both national hospitalisation and South Australian notification data. The decline in varicella hospitalisations commenced from 2004, when vaccine was available but not funded, and continued after it was added to the National Immunisation Program in November 2005. The impact is most marked in children aged 12–23 months, 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. Additionally, trends in disease epidemiology will need to be reviewed through notification data from other Australian states and territories, and via other mechanisms, such as reporting to the Australian Paediatric Surveillance Unit of data on neonatal, congenital and severe varicella infections.
The epidemiology of herpes zoster, as reflected in the national hospitalisation data and notification data from South Australia, does not appear to have changed over this review period. Studies based on modelling have predicted an increase in herpes zoster as the circulation of wild varicella infection declines following vaccination.16 In light of this and with the anticipated increase in uptake of the zoster vaccine over time in older Australians, more comprehensive monitoring of trends in zoster occurrence, particularly trends in age-specific hospitalisations, would be valuable for evaluation of the impacts of both the varicella program in children and any subsequent zoster program.
In the pre-vaccine era rotavirus infection was the cause of approximately 10,000 hospitalisations per year in Australia.17,18 International estimates of the sensitivity of coding for rotavirus among gastroenteritis hospitalisations range from 25% to 47%.19-21 The data presented here for Australia are within that range. Publicly funded vaccine was available in the Northern Territory from October 2006 and nationally from July 2007. Therefore, the hospitalisation data presented here, up to June 2007, cover only the pre-vaccine period, with the exception of a 9-month period in the Northern Territory. The data show year-to-year variation in the pre-vaccine era, higher in 2006–2007 than the previous year. Notification data are available for this period only from the Northern Territory, and they show a lower rate in 2007 compared to 2006, possibly due to vaccine introduction, but more data are required before a firm conclusion can be drawn. Immunisation of infants in the first 6 months of life under the NIP should prevent the majority of severe cases of rotavirus and it is anticipated that hospitalisation rates will be substantially reduced. However, it is important to encourage timeliness of vaccination in order to ensure a maximal impact upon disease. Sufficient data should be available in the near future to provide a clearer picture of vaccine impact.