1. Immunisation and Counter-Measures Division, National Infection Service, Public Health England, London, United Kingdom
2. Statistics, Modelling and Economics Department, Public Health England, London, United Kingdom
3. Tuberculosis; Acute Respiratory, Gastrointestinal, Emerging and Zoonotic Infections; and Travel and Migrant Health Division (TARGET), National Infection Service, Public Health England, London, United Kingdom
4. Paediatric Infectious Disease Research Group St. George’s University of London, Cranmer Terrace, London, United Kingdom