This report demonstrates again the value of routinely collected data in monitoring the impact of Australia’s National Immunisation Program. Hospitalisation and death data from the Australian Institute of Health and Welfare (AIHW) National Hospital Morbidity Database and National Mortality Database provide important information on more severe disease, while the National Notifiable Diseases Surveillance System (NNDSS) of the Communicable Diseases Network Australia provides data that include less severe cases that are often more specific due to the common use of laboratory confirmation. National standardisation of NNDSS data, including case definitions and field codes, continues to expand. While general demographic data are generally complete, the completeness of some important fields in the notification records is more variable, such as Indigenous status, vaccination status and serogroup/subtype. This is often a reflection of the limited resources available to follow up cases to collect information, resources which are focused on particular diseases and/or age groups and geographic regions. ‘Enhanced’ surveillance data (additional clinical and/or laboratory data) are collected nationally for Hib and pneumococcal notifications, but not for other important diseases such as pertussis or meningococcal disease.
Two vaccines became available under the NIP shortly before (varicella vaccine) or within (rotavirus vaccine) the period covered by this report. For both varicella and rotavirus, notification status varied by jurisdiction, and there were insufficient data at national level to merit inclusion for this time period. Indeed, laboratory-based notification of cases has significant limitations for both these diseases, and other sources of routinely collected data, in particular emergency department presentations, have been harnessed in recent years to provide useful epidemiologic information on a number of infectious diseases. Especially with validation, emergency department presentations could be a valuable source of trends post program introduction for varicella, rotavirus and influenza.
Augmentation of routinely collected data by other more active surveillance systems is also likely to continue and increase. These systems currently include the Australian Paediatric Surveillance Unit, the Paediatric Active Enhanced Disease Surveillance pilot study, and general practice sentinel surveillance through the Australian Sentinel Practice Research Network. In the future, data quality and quantity, as well as efficiency of collection, could be improved through data linkage, by using information already collected on individuals from a range of sources. For example, linkage of the Australian Childhood Immunisation Register to morbidity and mortality data would greatly enhance the quality of vaccination status data for children as well as eliminating the resource-intensive re-collection of the information. Other electronic sources are likely to become important in the future as well, such as electronic health records, and increased availability of data linkage across multiple data sources offers great potential.