1. WHO Collaborating Center for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China
2. WHO Collaborating Center for Reference and Research on Influenza, Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
3. Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles, Los Angeles, California