1. Department of Infection, Immunity and Inflammation, Institute of Child Health, University College London, London, UK
2. Faculty of Medicine, Imperial College London, London, UK
3. Department of Haematology, Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, UK
4. Population, Policy & Practice Research and Teaching Department, Great Ormond Street Institute of Child Health, University College London, London, UK
5. Department of Infectious Disease, Faculty of Medicine, Imperial College London, London, UK
6. Department of Infectious Disease, Imperial College NHS Healthcare Trust, St Mary's Hospital, London, UK