1. Medical Research Council Centre for Outbreak Analysis and Modelling, School of Public Health, Imperial College London, Norfolk Place, London W2 1PG, UK.
2. Oxford University Clinical Research Unit, Hospital for Tropical Diseases, 764 Võ Vǎn Kiêt, District 5, Ho Chi Minh City 748010, Vietnam.
3. School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia.
4. Hospital for Tropical Diseases, 190 Ben Hám Tú, District 5, Ho Chi Minh City 748010, Vietnam.
5. Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford OX1 7FZ, UK.
6. Department of Microbiology and Immunology and Nossal Institute of Global Health, University of Melbourne, Carlton, Victoria 3010, Australia.