title: Pandemic influenza: an unresolved problem in prevention.
mesh_terms: D004196:Disease Outbreaks / Q000266:history; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D007114:Immunization; D007251:Influenza, Human / Q000453:epidemiology / Q000401:mortality / Q000517:prevention & control*; D006113:United Kingdom; D014481:United States