1. National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children’s Hospital Westmead, Sydney, Australia.
2. School of Public Health and Community Medicine, University of New South Wales, Samuels Bldg, Botany St, Randwick, Sydney 2052, Australia.
3. Vaccine Preventable Disease Surveillance, Department of Health, Canberra, Australia.
4. National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia.