title: Return and reformation after a century -- from 1918 to 2009 H1N1.
authors.forename: Xiaoxue
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000818:Animals; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics* / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology / Q000266:history / Q000821:virology; D013552:Swine / Q000821:virology