European Centre for Disease Prevention and Control, European Centre for Disease Prevention and Control, European Centre for Disease Prevention and Control, European Centre for Disease Prevention and Control, Superintendence of Public Health - Infectious Disease Prevention and Control Unit, Superintendence of Public Health, Superintendence of Public Health - Infectious Disease Prevention and Control Unit, National Institute of Public Health (Prague) - Department of Biostatistics, National Institute of Public Health (Prague) - Department of Biostatistics, National Institute of Public Health (Czech Republic) - Department of Infectious Diseases Epidemiology, National Institute of Public Health (Prague) - Department of Biostatistics, Norwegian Institute of Public Health - Division of Infection Control and Environmental Health, Norwegian Institute of Public Health - Division of Infection Control and Environmental Health, Norwegian Institute of Public HealthNorwegian Institute of Public Health - Division of Infection Control and Environmental Health, Norwegian Institute of Public Health - Division of Infection Control and Environmental Health, Health Directorate, Luxembourg, Health Directorate, Luxembourg, Health Directorate, Luxembourg, Health Protection Surveillance Centre (HPSC), Health Protection Surveillance Centre (HPSC), Health Protection Surveillance Centre (HPSC), Health Protection Surveillance Centre (HPSC), World Health Organization (WHO) - World Health Organization Regional Office for Europe, World Health Organization (WHO) - World Health Organization Regional Office for Europe and European Centre for Disease Prevention and Control

Epiconcept - Epidemiology Department, Epiconcept, National Health Institute Doutor Ricardo Jorge (INSA) - Epidemiology Department, Carlos III Institute of Health, Health Protection Surveillance Centre (HPSC), Sorbonne University - Institut Pierre Louis d'Épidémiologie et de Santé Publique IPLESP, Universidad Pública de Navarra - IdiSNA, Navarra Institute for Health Research, Robert Koch Institute, NIVEL (Netherlands Institute for Health Services Research), National Health Institute Doutor Ricardo Jorge (INSA) - Epidemiology Department, Semmelweis University, Public Health Agency of Sweden, Croatian Institute of Public Health, Cantacuzino National Military Medical Institute for Research and Development, Epiconcept, Consejería de Sanidad - Dirección General de Salud Pública, University College Dublin (UCD), University of Paris-Saclay - Laboratoire de Microbiologie, Universidad Pública de Navarra - IdiSNA, Navarra Institute for Health Research, Robert Koch Institute, National Institute for Public Health and the Environment (RIVM) - Centre for Infectious Disease Control, National Institute of Health Doutor Ricardo Jorge, Semmelweis University, Public Health Agency of Sweden, Croatian Institute of Public Health, National Institute for Public Health and the Environment (RIVM), National Institute of Health Doutor Ricardo Jorge, European Centre for Disease Prevention and Control, European Centre for Disease Prevention and Control and Epiconcept

European Centre for Disease Prevention and Control, Carlos III Institute of Health - National Center for Epidemiology, Public Health Agency of Sweden, Carlos III Institute of Health - Communicable Diseases Department, National Institute of Public Health Romania-National Centre for Communicable Diseases Surveillance and Control, Sciensano - Department of Epidemiology and Public Health, Sciensano, National Institute of Public Health (Czech Republic) - Department of Infectious Diseases Epidemiology, National Institute of Public Health (Czech Republic) - Department of Infectious Diseases Epidemiology, Public Health Agency of Sweden, National Health Institute Doutor Ricardo Jorge (INSA) - National Influenza Reference Laboratory, Medical University of Vienna - Department of Virology, Superintendence of Public Health - Infectious Disease Prevention and Control Unit, Superintendence of Public Health - Infectious Disease Prevention and Control Unit, National Institute for Public Health and the Environment (RIVM), National Institute for Public Health and the Environment (RIVM), Health Protection Surveillance Centre (HPSC), Health Protection Surveillance Centre (HPSC) and Government of the United States of America - Centers for Disease Control and Prevention (CDC)