1 Vaccine Preventable Diseases Surveillance Section, Health Protection Policy Branch, Office of Health Protection, Department of Health, Canberra, Australian Capital Territory.
2 WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Victoria.
3 Communicable Disease Epidemiology and Surveillance, Health Protection Branch, Regulation, Health Protection and Emergency Management Division, Department of Health and Human Services, Melbourne, Victoria.
4 Communicable Disease Control Branch, SA Department of Health and Ageing, Adelaide, South Australia.