1 Department of Paediatric Infectious Diseases, St. George's Hospital, Blackshaw Road, London SW17 0QT, UK; Immunisation Division, UK Health Security Agency, 61 Colindale Avenue, London, UK. Electronic address: borbala.zsigmond@gmail.com.
2 Department of Infection, St George's University Hospitals NHS Foundation Trust, London, UK; Immunisation Division, UK Health Security Agency, 61 Colindale Avenue, London, UK.
3 Institute of Infection and Immunity, St George's University of London, UK; Immunisation Division, UK Health Security Agency, 61 Colindale Avenue, London, UK.
4 Department of Paediatric Infectious Diseases, St. George's Hospital, Blackshaw Road, London SW17 0QT, UK; Department of Infection, St George's University Hospitals NHS Foundation Trust, London, UK; Institute of Infection and Immunity, St George's University of London, UK; Immunisation Division, UK Health Security Agency, 61 Colindale Avenue, London, UK.