Carlos III Institute of Health - Communicable Diseases Department, Carlos III Institute of Health - CIBER de Epidemiología y Salud Pública (CIBERESP), Madrid Ministry of Health - Vaccines Division, Carlos III Institute of Health - Communicable Diseases Department, Madrid Ministry of Health - Centre for the Coordination of Health Alerts and Emergencies, Madrid Ministry of Health - Vaccines Division, Spanish Agency for Medicines and Medical Devices (AEMPS), Carlos III Institute of Health - Communicable Diseases Department and Harvard University - CAUSALab

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)

Carlos III Institute of Health - Cancer and Environmental Epidemiology Unit, Carlos III Institute of Health, Carlos III Institute of Health - Communicable Diseases Department, Carlos III Institute of Health - Communicable Diseases Department, Carlos III Institute of Health - Communicable Diseases Department, Carlos III Institute of Health - Communicable Diseases Department and Carlos III Institute of Health - Communicable Diseases Department