Pam Sonnenberg, MB BCh, MSc, PhD1, Catherine Ison, PhD2, Nigel Field, MB PhD3, Soazig Clifton, BSc3, Clare Tanton, PhD3, Kate Soldan, PhD2, Simon Beddows, PhD2, Cath Mercer, BSc, MSc, PhD1 and Anne Johnson, MBBS, MD3, 1Department of Infection and Population Health, University College London, London, United Kingdom, 2National Centre for Infectious Disease Surveillance and Control (CIDSC), Public Health England, London, United Kingdom, 3Research Department of Infection and Population Health, University College London, London, United Kingdom