1 Chatham House Centre on Global Health Security, Royal Institute of International Affairs, London, UK; Public Health Strategy Division, Public Health England, London, UK.
2 King's Sierra Leone Partnership, Freetown, Sierra Leone; Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK.
3 Chatham House Centre on Global Health Security, Royal Institute of International Affairs, London, UK; Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK. Electronic address: david.heymann@lshtm.ac.uk.