2 UK Health Security Agency, London, UK; NIHR Health Protection Research Unit in Vaccines and Immunisation, London School of Hygiene & Tropical Medicine, London, UK.
3 UK Health Security Agency, London, UK; NIHR Health Protection Research Unit in Respiratory Infections, Imperial College London, London, UK.
4 UK Health Security Agency, London, UK; Paediatric Infectious Diseases Research Group, St George's University of London, London, UK. Electronic address: [email protected].