1. Paediatric Infectious Diseases Research Group, St. George’s University of London, London, United Kingdom
2. Immunisation Division, UK Health Security Agency, London, United Kingdom
3. UK Health Security Agency East of England Health Protection Team, Mildenhall, United Kingdom
4. UK Health Security Agency, South London Health Protection Team and the London Coordination and Response Cell, London, United Kingdom
5. UK Health Security Agency Northwest London Health Protection Team and the London Coordination and Response Cell, London, United Kingdom
6. Paediatric Infectious Diseases Department, Imperial College London, London, United Kingdom
7. Paediatric Immunology and Infectious Diseases, Evelina London Children's Hospital, London, United Kingdom
8. Clinical and Public Health Group, UK Health Security Agency, London, United Kingdom