University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University College London - UCL Institute of Education, University of Cambridge and University of Sydney - National Centre for Immunisation Research and Surveillance

Government of the United Kingdom - Public Health England, UK Health Security Agency, UK Health Security Agency - Emergency Preparedness, Response and Resilience, Government of the United Kingdom - Public Health England, UK Health Security Agency, Government of the United Kingdom - Public Health England, NHSE/I Children and Young People's Transformation Team, affiliation not provided to SSRN, University College London - Great Ormond Street Institute of Child Health, Cedars Sinai Medical Center - Department of Pediatrics, Government of the United Kingdom - Public Health England, UK Health Security Agency, Public Health England - Immunisation and Countermeasures Division, Royal College of Paediatrics and Child Health, University of Southampton - University Hospital Southampton NHS Foundation Trust, University Hospitals Bristol - University Hospitals Bristol and Weston NHS Foundation Trust, St George's University Hospitals NHS Foundation Trust, Birmingham Women’s and Children’s NHS Foundation Trust, Royal College of Paediatrics and Child Health, NHS Foundation Trust - London North West Healthcare NHS Trust, Alder Hey Children's NHS Foundation Trust, Public Health England, University of Bristol, Public Health England - Immunisation, Hepatitis, and Blood Safety Department, University of Liverpool - Health Protection Research Unit in Emerging and Zoonotic Infections, University of Edinburgh - Department of Child Life and Health, Imperial College Healthcare NHS Trust - Paediatric Infectious Diseases Department, Anuerin Bevan University Health Board, Government of the United Kingdom - Public Health Scotland and Public Health England - Immunisation and Countermeasures Division

University College London - Great Ormond Street Institute of Child Health, University of Cambridge - Department of Medicine, University of Cambridge, Children’s Hospital at Westmead - The National Centre for Immunisation Research and Surveillance (NCIRS), Public Health England - Immunisation and Countermeasures Division, University of Oxford, London School of Hygiene & Tropical Medicine and University of Exeter - Medical School

University of Edinburgh, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University of Leicester, University College London - Great Ormond Street Institute of Child Health, Public Health England - Immunisation and Countermeasures Division, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health and University of Edinburgh - Department of Child Life and Health

University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health, University of Oxford, Queen Mary University of London, University of Surrey, Imperial College London - Division of Psychiatry, Leicester University, University College London, University College London - Great Ormond Street Institute of Child Health, University College London - Great Ormond Street Institute of Child Health and University College London