1Statistics, Modelling and Economics Department, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom
2Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease epidemiology, Imperial College School of Public Health, London, United Kingdom
3Respiratory Diseases Department, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom
4The Francis Crick Institute, Mill Hill Laboratory, The Ridgeway, Mill Hill, London, NW7 1AA, United Kingdom