1 Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK; MRC Centre for Outbreak Analysis and Modelling, and NIHR Health Protection Research Unit in Modelling Methodology, Imperial College London, London, UK; Modelling and Economics Unit, National Infection Service, Public Health England, London, UK. Electronic address: p.white@imperial.ac.uk.
2 Institute for Global Health, University College London, London, UK; Medical Directorate, Public Health England, London, UK.