1 Communicable Diseases Policy Research Group, London School of Hygiene & Tropical Medicine, London, UK; Saw Swee Hock School of Public Health, National University of Singapore, Singapore 117549, Singapore. Electronic address: mishal.khan@lshtm.ac.uk.
2 Saw Swee Hock School of Public Health, National University of Singapore, Singapore 117549, Singapore; Center for Economic and Social Research, University of Southern California, Los Angeles, CA, USA.
3 Saw Swee Hock School of Public Health, National University of Singapore, Singapore 117549, Singapore.
4 Communicable Diseases Policy Research Group, London School of Hygiene & Tropical Medicine, London, UK; Saw Swee Hock School of Public Health, National University of Singapore, Singapore 117549, Singapore; Faculty of Public Health, Mahidol University, Bangkok, Thailand.