London School of Hygiene & Tropical Medicine - Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine - Population Studies Group, London School of Hygiene & Tropical Medicine - Population Studies Group, University of Edinburgh - Centre for Global Health Research, London School of Hygiene & Tropical Medicine - Medical Research Council Unit The Gambia, Africa Health Research Institute, Kenya Medical Research Institute (KEMRI) - Kenya Medical Research Institute (KEMRI)/Walter Reed Project, Kenya Medical Research Institute (KEMRI) - Kenya Medical Research Institute (KEMRI)/Walter Reed Project, Kenya Medical Research Institute (KEMRI) - Kenya Medical Research Institute (KEMRI)/Walter Reed Project, Aga Khan University - Centre of Excellence in Women and Child Health, King’s College London - Department of Women and Children’s Health, King’s College London - Department of Women and Children’s Health and London School of Hygiene & Tropical Medicine - Department of Infectious Disease Epidemiology