1 Respiratory Sciences, University of Leicester, Leicester, UK. Electronic address: Jwtang49@hotmail.com.
2 JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China; Stanley Ho Centre for Emerging Infectious Diseases, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China; Hong Kong Institute of Asia-Pacific Studies, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China; Shenzhen Research Institute of the Chinese University of Hong Kong, Shenzhen, China.