1 Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. Electronic address: isq8@cdc.gov.
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, China; Laboratory of Data Discovery for Health, Hong Kong Science and Technology Park, Hong Kong Special Administrative Region, China.