1. Global Health Policy Unit, School of Social and Political Science, University of Edinburgh , 15a George Square, Edinburgh, EH8 9LD , UK
2. Department of Public Health, Environments and Society, Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine , 15-17 Tavistock Place, London WC1H 9SH , UK
3. Department of Health Services Research and Policy, Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine , 15-17 Tavistock Place, London WC1H 9SH , UK
4. UK PRP SPECTRUM Consortium, Usher Institute, Old Medical School, University of Edinburgh , Teviot Place, Edinburgh EH8 9AG , UK