title: Prior infection with classical swine H1N1 influenza viruses is associated with protective immunity to the 2009 pandemic H1N1 virus.
abstract: BACKGROUND
  The 2009 H1N1 pandemic emerged even though seasonal H1N1 viruses have circulated for decades. Epidemiological evidence suggested that the current seasonal vaccine did not offer significant protection from the novel pandemic, and that people over the age of 50 were less susceptible to infection.
  
  
  OBJECTIVE
  In a mouse challenge study with the 2009 pandemic H1N1 virus, we evaluated protective immune responses elicited by prior infection with human and swine influenza A viruses.
  
  
  RESULTS
  Mice infected with A/Mexico/4108/2009 (Mex09) showed significant weight loss and 40% mortality. Prior infection with a 1976 classical swine H1N1 virus resulted in complete protection from Mex09 challenge. Prior infection with either a 2009 or a 1940 seasonal H1N1 influenza virus provided partial protection and a >100-fold reduction in viral lung titers at day 4 post-infection.
  
  
  CONCLUSIONS
  These findings indicate that in experimental animals recently induced immunity to 1918-derived H1N1 seasonal influenza viruses, and to a 1976 swine influenza virus, afford a degree of protection against the 2009 pandemic virus. Implications of these findings are discussed in the context of accumulating data suggesting partial protection of older persons during the 2009 pandemic.
authors.affiliation: Viral Pathogenesis and Evolution Section, Laboratory of Infectious Diseases, Bethesda, MD 20892-3203, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Kash
authors.forename: Li
authors.initials: L
authors.lastname: Qi
authors.forename: Vivien G
authors.initials: VG
authors.lastname: Dugan
authors.forename: Brett W
authors.initials: BW
authors.lastname: Jagger
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Hrabal
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Memoli
authors.forename: David M
authors.initials: DM
authors.lastname: Morens
authors.forename: Jeffery K
authors.initials: JK
authors.lastname: Taubenberger
mesh_terms: D000818:Animals; D056738:Cross Protection; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D008168:Lung / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009976:Orthomyxoviridae Infections / Q000517:prevention & control*; D012367:RNA, Viral / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D012367:RNA, Viral
references.citation: J Infect Dis. 1998 Jul;178(1):53-60
references.pmid: 9652423
references.citation: Nature. 2009 Aug 20;460(7258):1021-5
references.pmid: 19672242
references.citation: Emerg Infect Dis. 2006 Jan;12(1):29-33
references.pmid: 16494713
references.citation: Vaccine. 2009 Aug 6;27(36):4983-9
references.pmid: 19538996
references.citation: N Engl J Med. 2009 Nov 12;361(20):1945-52
references.pmid: 19745214
references.citation: J Virol. 2009 Jun;83(11):5485-94
references.pmid: 19297491
references.citation: Science. 2009 Jul 10;325(5937):197-201
references.pmid: 19465683
references.citation: Philos Trans R Soc Lond B Biol Sci. 2001 Dec 29;356(1416):1829-39
references.pmid: 11779381
references.citation: Med J Aust. 2009 Aug 3;191(3):146-9
references.pmid: 19645642
references.citation: J Virol. 2008 Feb;82(3):1350-9
references.pmid: 18032492
references.citation: Vaccine. 2007 Jan 8;25(4):612-20
references.pmid: 17005299
references.citation: Philos Trans R Soc Lond B Biol Sci. 2001 Dec 29;356(1416):1871-6
references.pmid: 11779386
references.citation: Cell. 1982 Dec;31(2 Pt 1):417-27
references.pmid: 6186384
references.citation: MMWR Morb Mortal Wkly Rep. 2009 May 22;58(19):521-4
references.pmid: 19478718
references.citation: J Immunol. 2007 Jan 15;178(2):1030-8
references.pmid: 17202366
references.citation: Virology. 1999 Feb 1;254(1):50-60
references.pmid: 9927573
references.citation: N Engl J Med. 2009 Jul 16;361(3):225-9
references.pmid: 19564629
references.citation: Curr Protoc Microbiol. 2006 Dec;Chapter 15:Unit 15G.1
references.pmid: 18770580
references.citation: Euro Surveill. 2009 Aug 20;14(33):
references.pmid: 19712643
references.citation: Bull N Y Acad Med. 1979 Mar;55(3):285-302
references.pmid: 369639
references.citation: J Virol. 2009 Apr;83(8):3754-61
references.pmid: 19211766
references.citation: N Engl J Med. 2009 Jun 18;360(25):2605-15
references.pmid: 19423869
references.citation: MMWR Morb Mortal Wkly Rep. 2009 Aug 28;58(33):913-8
references.pmid: 19713879
references.citation: Euro Surveill. 2009 Aug 27;14(34):
references.pmid: 19712648
references.citation: Proc Natl Acad Sci U S A. 1991 May 15;88(10):4270-4
references.pmid: 1840695
references.citation: Proc Natl Acad Sci U S A. 2004 Mar 2;101(9):3166-71
references.pmid: 14963236