1 Clinical Research Department, London School of Hygiene & Tropical Medicine, London, UK; Malawi Liverpool Wellcome Programme, Blantyre, Malawi.
2 Public Health Data Science Research Group, UCL Institute of Health Informatics, University College London, London NW1 2DA, UK; Division of Infection and Immunity, University College London, London, UK. Electronic address: t.yates@ucl.ac.uk.