1. Immunisation and Countermeasures Division, Public Health England, London, United Kingdom
2. Respiratory and Vaccine Preventable Bacterial Reference Unit (RVBRU), Public Health England, London, United Kingdom
3. Statistics, Modelling, and Economics Department, Public Health England, London, United Kingdom
4. London School of Hygiene and Tropical Medicine, London, United Kingdom
5. Paediatric Infectious Diseases Research Group (PIDRG), St George’s University of London, London, United Kingdom