Pablo Cuesta, Alberto del Castillo, Thomas Rowe, Raquel Almansa, José María Eiros, Paula Ramirez, Silvia Rojo, Alberto Tenorio-Abreu, Isabel Gonzalez, Mario Rodríguez-Domínguez, José Manuel Gómez, Carlos J.Lopez, Ignacio Martin-Loeches, Maria C Gallegos, Raúl Ortiz de Lejarazu, Juan Carlos Galán, Aurora Lietor, Elia Sanchez, Rafael Cantón, Jordi Rello, Monica Gordon, David Banner, Carmen Hinojosa, Maria J. Ramos, David Varillas, Victoria Fernández, David J. Kelvin, S Huidobro, M. Lourdes Molina, Nuria Torner, Alberto J. Leon, Jesus F. Bermejo-Martin, M. A. Marcos, Beatriz Villanueva, Carlos Serón, Tomás Pumarola, Dariela Micheloud, [Bermejo-Martin,JF, Ortiz de Lejarazu,R, Almansa,R, Varillas,D, Rojo,S, Eiros,JM] National Centre of Influenza, Hospital Clínico Universitario de Valladolid, Valladolid, Spain. [Bermejo-Martin,JF, Eiros,JM] Unidad de Investigación en Infección e Inmunidad- Microbiology Service, Hospital Clínico Universitario de Valladolid- IECSCYL, Valladolid, Spain. [Pumarola,T, Marcos,MA] Virology Laboratory, Hospital Clinic de Barcelona, Barcelona. [Rello,J, Martin-Loeches,I] Critical Care Department, Joan XXIII University Hospital-CIBERes Enfermedades Respiratorias-IISPV. Tarragona, Spain. [Ramírez,P, Gordón,M] Critical Care Department, Hospital Universitario La Fe, Spain. [Gallegos,MC, Fernández,V] Microbiology Service, Hospital Son Llatzer, Palma de Mallorca, Spain. [Serón,C] Intensive Care Unit, Hospital General San Jorge, Huesca, Spain. [Micheloud,D, Gomez,JM] Intensive Care Unit & Internal Medicine Service, Hospital Gregorio Marañón, Madrid, Spain. [Tenorio-Abreu,A, Ramos,MJ] Microbiology Service, Hospital Universitario de Canarias, Santa Cruz De Tenerifey, Spain. [Molina,ML] Microbiology Service, Hospital General de La Palma, Breña Alta, Spain. [Huidobro,S] Intensive Care Unit, Hospital Universitario de Canarias, Santa Cruz De Tenerifeý, Spain. [Sanchez,E] Intensive Care Unit, Hospital Virgen del Rocío, Sevilla, Spain. [Del Castillo,A] Intensive Care Unit Service, Hospital Son Llatzer, Palma de Mallorca, Spain. [Villanueva,V, López,CJ] Intensive Care Unit Service, Hospital Lozano Blesa, Zaragoza, Spain. [Rodríguez-Domínguez,M, Galan,JC, Cantón,R] Microbiology Service, Hospital Universitario Ramón y Cajal & CIBERESP, Madrid, Spain. [Lietor,A] Intensive Care Unit, Hospital Universitario Ramón y Cajal, Madrid, Spain. [Hinojosa,C, Gonzalez,I] Infectious Diseases Service, Hospital Clínico Universitario, Valladolid, Spain. [Torner,N] Preventive Medicine Service, Hospital Universitario Valle Hebron & CIBERESP, Barcelona, Spain. [Banner,D, Rowe,T, Kelvin,DJ] Experimental Theraputics Division, University Health Network, Medical Discovery Tower, Toronto,Canada. [Leon,A, Kelvin,DJ] International Institute of Infection and Immunity, Shantou University, Shantou, Guangdong Province, PR China. [Cuesta,P] Intensive Care Unit, Hospital de Villarobredo, Villarrobledo, Spain. [Rowe,T, Kelvin,DJ] Department of Immunology, University of Toronto, Medical Discovery Tower, Toronto, Canada., and This work was possible thanks to the financial support obtained from the Ministry of Science of Spain and Consejería de Sanidad Junta de Castilla y León, Programa de Investigación comisionada en gripe, GR09/0021, Programa para favorecer la incorporación de grupos de investigación en las Instituciones del Sistema Nacional de Salud, EMER07/050, and Proyectos en Investigación Sanitaria, PI081236. CIHR, NIH and LKSF-Canada support DJK.