1 WHO Collaborating Centre for Reference and Research on Influenza, Peter Doherty Institute for Infection and Immunity, 792 Elizabeth St, Melbourne, VIC 3000, Australia; Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles, USA. Electronic address: [email protected].
2 WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region.
3 Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles, USA; Department of Statistics, UCLA College of Letters and Science, University of California, Los Angeles, USA.