1 MRC Centre for Outbreak Analysis and Modelling and NIHR Health Protection Research Unit in Modelling Methodology, Imperial College London, London, W2 1PG, UK.
2 Department of Immunology and Infectious Diseases, Harvard TH Chan School of Public Health, Boston, MA, USA; Division of Infectious Diseases, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
3 MRC Centre for Outbreak Analysis and Modelling and NIHR Health Protection Research Unit in Modelling Methodology, Imperial College London, London, W2 1PG, UK; Modelling and Economics Unit, National Infection Service, Public Health England, London, UK. Electronic address: p.white@imperial.ac.uk.