The University of Hong Kong - WHO Collaborating Centre for Infectious Disease Epidemiology and Control, The Chinese University of Hong Kong (CUHK) - Department of Medicine & Therapeutics, Princess Margaret Hospital - Department of Medicine, Queen Elizabeth Hospital, Hong Kong - Department of Paediatrics, Princess Margaret Hospital - Department of Paediatric and Adolescent Medicine, The University of Hong Kong, The University of Hong Kong, The University of Hong Kong, The University of Hong Kong - School of Public Health, The University of Hong Kong - School of Public Health, The University of Hong Kong - School of Public Health, The University of Hong Kong - School of Public Health and The University of Hong Kong - School of Public Health