Frank H Beard1, Julie Leask2, Peter B McIntyre3. 1. National Centre for Immunisation Research and Surveillance, The Children's Hospital at Westmead, Sydney, NSW peter.mcintyre@health.nsw.gov.au. 2. School of Public Health, University of Sydney, Sydney, NSW. 3. National Centre for Immunisation Research and Surveillance, The Children's Hospital at Westmead, Sydney, NSW.