University of Oxford, University of Oxford, Liverpool School of Tropical Medicine, Kenya Medical Research Institute (KEMRI) - Kemri-Wellcome Trust Research Programme, Kenya Medical Research Institute (KEMRI) - Kemri-Wellcome Trust Research Programme, Kemri-Wellcome Trust Research Programme - Clinical Research Department,, University of Oxford - KEMRI-Coast Centre for Geographical Medicine and Research, affiliation not provided to SSRN, NHS Foundation Trust - Oxford University Hospitals, Kenya Medical Research Institute (KEMRI) - Kemri-Wellcome Trust Research Programme, University of Oxford - Centre for Tropical Medicine and Global Health, London School of Hygiene & Tropical Medicine - Faculty of Epidemiology and Population Health, Kenya Medical Research Institute (KEMRI) - Kemri-Wellcome Trust Research Programme, University of Oxford - Peter Medawar Building for Pathogen Research and Kenya Medical Research Institute (KEMRI) - Kemri-Wellcome Trust Research Programme