1. aResearch Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London, WC1E 6BT, England.
2. bResearch Department of Infection and Population Health, University College London, London, England.
3. cNational Institute for Health and Clinical Excellence, London, England.
4. dLondon School of Hygiene and Tropical Medicine, London, England.
5. eDivision of Health and Social Care Research, King’s College London, London, England.
6. fDepartment of Epidemiology and Public Health, Imperial College London, London, England.
7. gDepartment of Geography, Durham University, England.