1. Department of Paediatrics and Adolescent Medicine, Queen Mary Hospital and Li Ka Shing Faculty of Medicine, The University of Hong Kong
2. Department of Paediatrics and Adolescent Medicine, Princess Margaret Hospital
3. WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health
4. Department of Microbiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong
5. Department of Pathology, Princess Margaret Hospital
6. Department of Pathology, Yan Chai Hospital
7. Center of Influenza Research, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China