Department of Infectious Disease, Division of Medicine, Institute of Global Health and Innovation, Imperial College, London, UK. Uganda Blood Transfusion Services (BTS), National BTS, Kampala, Uganda. Department of Paediatrics and Child Health, School of Medicine, Makerere University and Mulago Hospital, Kampala, Uganda. Faculty of Health Sciences, Busitema University, Mbale Regional Referral Hospital, Mbale, Uganda. College of Medicine, Malawi-Liverpool-Wellcome Research Programme, Blantyre, Malawi. Soroti Regional Referral Hospital, Soroti, Uganda. Kenya Medical Research Institute (KEMRI)/Wellcome Trust Research Programme, Kilifi, Kenya. Malawi BTS, Blantyre, Malawi. Liverpool School of Tropical Medicine, Liverpool, UK. Haematology & Transfusion Service, Centre Hospitalier et Universitaire, Yaounde, Cameroon. Medical Research Council Clinical Trials Unit (MRC CTU), University College London, London, UK.