London School of Hygiene & Tropical Medicine, University Hospitals Bristol - University Hospitals Bristol NHS Foundation Trust, University Hospitals Bristol - University Hospitals Bristol NHS Foundation Trust, Government of the United States of America - Centers for Disease Control and Prevention (CDC), University of Melbourne - Murdoch Children's Research Institute, Government of the United States of America - Centers for Disease Control and Prevention (CDC), All India Institute of Medical Sciences (AIIMS) - Department of Paediatrics, British Columbia Centre for Disease Control, Stellenbosch University - Department of Paediatrics and Child Health, Santé Publique France - Infectious Diseases Department, Government of the United Kingdom - Public Health England, UK Health Security Agency - COVID-19 National Epidemiology Cell, Santé Publique France - Direction des Maladies Infectieuses, Government of the Republic of Finland - Infectious Disease Control and Vaccinations Unit, British Columbia Centre for Disease Control, Government of the United States of America - Centers for Disease Control and Prevention (CDC), University of Bergen - Department of Medicine, Norwegian Institute of Public Health - Department of Vaccine Preventable Diseases, Government of the United States of America - Artic Investigations Program and London School of Hygiene & Tropical Medicine