Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk|Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine, London, UK. taane.clark@lshtm.ac.uk