Immunisation and Vaccine Preventable Diseases,UK Health Security Agency, University College London - Centre for Perioperative Medicine, UCL 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 Cambridge - Department of Psychiatry, Research Department of Primary Care & Population Health, University College London Medical School, Imperial College Healthcare NHS Trust - Paediatric Infectious Diseases Department, University College London - Great Ormond Street Institute of Child Health, Suffolk University Law School, University College London - Great Ormond Street Institute of Child Health and Government of the United Kingdom - Immunisation and Countermeasures Division

Immunisation and Countermeasures Division, Public Health England, Government of the United Kingdom - Public Health England, Government of the United Kingdom - Public Health England, Joint Modelling Team, United Kingdom Health Security Agency, Public Health England - Immunisation and Countermeasures Division, Immunisation and Countermeasures Division, Public Health England, BPSU, Royal College of Paediatrics, BPSU, Royal College of Paediatrics, Paediatric Intensive Care Unit, Bristol Royal Hospital for Children, Department of congenital cardiology, University Hospital Southampton NHS Foundation Trust, BMBS, Alder Hey Children’s NHS Foundation Trust, Liverpool, Government of the United Kingdom - Birmingham Women’s and Children’s NHS Foundation Trust, Imperial College Healthcare NHS Trust - Paediatric Infectious Diseases Department, Paediatric Intensive Care Unit, St George’s Hospital, Public Health Scotland - Clinical and Public Health Intelligence Team, Public Health Wales, University of Edinburgh - Department of Child Life and Health, University of Liverpool - NIHR Health Protection Research Unit for Emerging and Zoonotic Infection, Public Health England - Immunisation, Hepatitis, and Blood Safety Department, Faculty of Medicine and Institute for Life Sciences, University of Southampton, University Hospitals Bristol NHS Foundation Trust, Government of the United Kingdom - Public Health England and Government of the United Kingdom - Immunisation and Countermeasures Division

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

Nottingham Children's Hospital - Paediatric Critical Care Unit, Evelina Children's Hospital - Paediatric Intensive Care Unit (PICU), Nottingham Children's Hospital - Paediatric Critical Care Unit, Nottingham Children's Hospital - Paediatric Critical Care Unit, Evelina Children's Hospital - Paediatric Intensive Care Unit (PICU), Great Ormond Street Hospital - Paediatric Intensive Care Unit, Great Ormond Street Hospital - Paediatric Intensive Care Unit, Birmingham Women’s and Children’s NHS Foundation Trust - Paediatric Intensive Care Unit, Royal Manchester Children's Hospital - Paediatric Intensive Care Unit, King's College Hospital - Paediatric Intensive Care Unit, Great Ormond Street Hospital - Paediatric Intensive Care Unit, Evelina Children's Hospital - Paediatric Intensive Care Unit (PICU), Leicester Royal Infirmary - Paediatric Intensive Care Unit, Leeds Royal Infirmary - Paediatric Intensive Care Unit, Children's Hospital for Wales - Paediatric Critical Care Unit, Southampton Children’s Hospital - Paediatric Intensive Care Unit, Alder Hey Children's Hospital - Paediatric Intensive Care Unit, Royal Hospital for Children - Paediatric Intensive Care Unit, St Mary’s Hospital - Paediatric Intensive Care Unit, John Radcliffe Hospital - Paediatric Critical Care Unit, Imperial College Healthcare NHS Trust - Paediatric Infectious Diseases Department, Nottingham Children's Hospital - Paediatric Critical Care Unit, St Mary’s Hospital - Paediatric Intensive Care Unit and Birmingham Women’s and Children’s NHS Foundation Trust - Paediatric Intensive Care Unit

Imperial College London, affiliation not provided to SSRN, affiliation not provided to SSRN, affiliation not provided to SSRN, Imperial College London - Department of Primary Care and Public Health, Imperial College Healthcare NHS Trust - Paediatric Infectious Diseases Department, Institute of Cancer Research (ICR), affiliation not provided to SSRN and Imperial College London