1 Center for Global Health and Department of Dermatology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA efreeman@mgh.harvard.edu.
2 The Centre for Mathematical Modelling of Infectious Diseases, London School of Hygiene and Tropical Medicine, London, UK.
3 Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA, USA.
4 Department of Prevention Programme and Knowledge Management, Nigeria Centre for Disease Control, Abuja, Nigeria.