Unseasonal Transmission of H3N2 Influenza A Virus During the Swine-Origin H1N1 Pandemic

Center for Vaccine Research, Department of Computational Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Journal of Virology (Impact Factor: 4.44). 03/2010; 84(11):5715-8. DOI: 10.1128/JVI.00018-10
Source: PubMed


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.

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Available from: Xudong Lin, Mar 06, 2015
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