1. World Health Organization Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, the University of Hong Kong, Hong Kong SAR, People’s Republic of China
2. World Health Organization Collaborating Centre for Reference and Research on Influenza at the 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
4. Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Victoria, Australia
5. Statistics Department, the Wharton School, University of Pennsylvania, Philadelphia, Pennsylvania