Unseasonal transmission of H3N2 influenza A virus during the swine-origin H1N1 pandemic

Elodie Ghedin, David E. Wentworth, Rebecca A. Halpin, Xudong Lin, Jayati Bera, Jay DePasse, Adam Fitch, Sara Griesemer, Erin Hine, Daniel A. Katzel, Larry Overton, Kathleen Proudfoot, Jeffrey Sitz, Bridget Szczypinski, Kirsten St George, David J. Spiro, Edward C. Holmes

Research output: Contribution to journalArticlepeer-review


The initial wave of swine-origin influenza A virus (pandemic H1N1/09) in the United States during the spring and summer of 2009 also resulted in an increased vigilance and sampling of seasonal influenza viruses (H1N1 and H3N2), even though they are normally characterized by very low incidence outside of the winter months. To explore the nature of virus evolution during this influenza "off-season," we conducted a phylogenetic analysis of H1N1 and H3N2 sequences sampled during April to June 2009 in New York State. Our analysis revealed that multiple lineages of both viruses were introduced and cocirculated during this time, as is typical of influenza virus during the winter. Strikingly, however, we also found strong evidence for the presence of a large transmission chain of H3N2 viruses centered on the south-east of New York State and which continued until at least 1 June 2009. These results suggest that the unseasonal transmission of influenza A viruses may be more widespread than is usually supposed.

Original languageEnglish (US)
Pages (from-to)5715-5718
Number of pages4
JournalJournal of virology
Issue number11
StatePublished - Jun 2010

ASJC Scopus subject areas

  • Microbiology
  • Immunology
  • Insect Science
  • Virology


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