1. National Centre of Epidemiology, Institute of Health Carlos III, Madrid, Spain
2. EpiConcept, Paris, France
3. Ciber Epidemiología y Salud Pública (CIBERESP), Ministry of Science and Innovation, Institute of Health Carlos III, Spain
4. National Influenza Centre-Madrid, National Centre for Microbiology, Institute of Health Carlos III, Madrid, Spain
5. Members of the team are listed at the end of the article