1 Centre for Global Health, Usher Institute, University of Edinburgh, Edinburgh, UK; Department of Population Health, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK.
2 Centre for Global Health, Usher Institute, University of Edinburgh, Edinburgh, UK.
3 Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK. Electronic address: wendy.graham@lshtm.ac.uk.