Imperial College London - Section of Paediatric Infectious Disease, Government of the United Kingdom - Institute of Cancer Research, Mater Dei Hospital, Imperial College London, affiliation not provided to SSRN, Fondazione Policlinico Universitario A. Gemelli IRCCS - Department of Woman and Child Health and Public Health, University of Padua - Department of Woman’s and Child’s Health, Imperial College London - Department of Epidemiology and Biostatistics, Imperial College London, Ospedale Paediatrico Meyer Firenze, Leicester University, Karolinska Institutet - Department of Global Public Health, Jean Verdier Hospital, University College Dublin (UCD) - Women’s and Children’s Health, Louis Mourier Hospital, Erasmus University Rotterdam (EUR) - Department of General Paediatrics, affiliation not provided to SSRN, Paracelsus Medical University Salzburg, Tallaght University Hospital, Children’s Health Ireland, University of Szeged - Albert-Szent Györgyi Medical Centre, Hospital Universitario Cruces, Medical University of Vienna, Sorbonne University - Pediatric Emergency Deparment, Government of the United Kingdom - Birmingham Women’s and Children’s NHS Foundation Trust, Ludwig Maximilian University of Munich (LMU), Lithuanian University of Health Sciences, Medical University of Graz, affiliation not provided to SSRN, University of the West of England (UWE), Coimbra Hospital and University Centre (CHUC), Hospital Dr. Fernando da Fonseca, Alder Hey Children's NHS Foundation Trust, Ondokuz Mayis University, Riga Stradins University, Centro Hospitalar Tondela-Viseu, Association Clinique et Thérapeutique Infantile du Val-de-Marne (ACTIV), Karolinska Institutet, Hacettepe University Medical School, Mersin City Training and Research Hospital, Barnaspitali Hringsins Children's Hospital, Hospital Río Hortega de Valladolid, Padua University and Hospital, Erasmus University Rotterdam (EUR) - Department of General Paediatrics, Erasmus University Rotterdam (EUR) - Department of General Paediatrics and Hôpital Robert Debré