Department of Zoology, University of Oxford, Oxford, United Kingdom, School of Life Sciences, University of Warwick, Coventry, United Kingdom.|Field Epidemiology Service (Birmingham), Public Health England, West Midlands, United Kingdom.|Emergency Response Unit, Public Health England, Porton Down, United Kingdom.|Field Epidemiology Service (Birmingham), Public Health England, West Midlands, United Kingdom.|School of Mathematics, Queen Mary University of London, London, United Kingdom, Warwick Mathematics Institute, University of Warwick, Coventry, United Kingdom.|Warwick Mathematics Institute, University of Warwick, Coventry, United Kingdom.|School of Life Sciences, University of Warwick, Coventry, United Kingdom, Warwick Mathematics Institute, University of Warwick, Coventry, United Kingdom.