Malawi Epidemiology and Intervention Research Unit (MEIRU), University of Glasgow - Medical Research Council (MRC), Malawi Epidemiology and Intervention Research Unit (MEIRU), Lancaster University, Lancaster University, London School of Hygiene & Tropical Medicine, Malawi Epidemiology and Intervention Research Unit (MEIRU), Malawi Epidemiology and Intervention Research Unit (MEIRU), Kamuzu University of Health Sciences, Kamuzu University of Health Sciences, Kamuzu University of Health Sciences, University of Glasgow - Medical Research Council (MRC), University of Glasgow - Centre for Virus Research (CVR), Public Health Institute of Malawi, Malawi Epidemiology and Intervention Research Unit (MEIRU) and Malawi Epidemiology and Intervention Research Unit (MEIRU)