1 Institute for Global Health Sciences, University of California, San Francisco, San Francisco, CA 94158, USA. Electronic address: michael.reid@ucsf.edu.
2 School of Medicine and Harvard T H Chan School of Public Health, Harvard University, Cambridge, MA, USA.
3 Faculty of Medicine, School of Public Health, Imperial College London, London, UK.
4 Institute for Global Health Sciences, University of California, San Francisco, San Francisco, CA 94158, USA.