Sukhyun Ryu1, Angela Chow2, Byung Chul Chun3. 1. Division of Infectious Disease Control, Gyeonggi Provincial Government, Suwon, Republic of Korea; 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, Hong Kong. 2. Department of Clinical Epidemiology, Office of Clinical Epidemiology, Analytics, and Knowledge, Tan Tock Seng Hospital, Singapore. 3. Department of Preventive Medicine, Korea University College of Medicine, Seoul, Republic of Korea. Electronic address: chun@korea.ac.kr.