MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Diseases Epidemiology, Imperial College London, London, United Kingdom. jlegrand@imperial.ac.uk|MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Diseases Epidemiology, Imperial College London, London, United Kingdom. jlegrand@imperial.ac.uk|MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Diseases Epidemiology, Imperial College London, London, United Kingdom. jlegrand@imperial.ac.uk|MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Diseases Epidemiology, Imperial College London, London, United Kingdom. jlegrand@imperial.ac.uk|MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Diseases Epidemiology, Imperial College London, London, United Kingdom. jlegrand@imperial.ac.uk|MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Diseases Epidemiology, Imperial College London, London, United Kingdom. jlegrand@imperial.ac.uk