Katherine E. Gallagher, London School of Hygiene & Tropical Medicine; Anthony Scott, London School of Hygiene & Tropical Medicine; Ifedayo Adetifa, KEMRI Wellcome Trust Research Programme; John Ojal, London School of Hygiene & Tropical Medicine; Shirine Voller, KEMRI Wellcome Trust Research Programme, and Wangeci Kagucia, KEMRI Wellcome Trust Research Programme