# 7435
Between 2005 and the end of 2010, the CDC documented 19 human infections by swine origin influenza viruses (SOIV) across the United States, 12 of which were trH1N1 viruses, 6 were trH3N2, and 1 was trH1N2.
In 2011 a new strain of swine influenza - originally dubbed trH3N2 but renamed H3N2v (swine variant influenza) in late 2011 – was discovered to have evolved in pigs.
What made this virus different from the earlier trH3N2 novel strains was that it was a reassortant swine H3N2 which had acquired the matrix (M) gene from the 2009 H1N1 pandemic virus.
Reassortant H3N2 virus detected in Pennsylvania & Indiana – Source CDC
We first heard about this new strain on Sept. 2nd, 2011, via an early release from the CDC’s MMWR.
That report described two young children – one in Indiana and another in Pennsylvania - who were infected by a new swine-origin H3N2 virus (see Swine-Origin Influenza A (H3N2) Virus Infection in Two Children --- Indiana and Pennsylvania, July--August 2011).
While these first two cases first appeared to be one-off, dead end transmissions, it was only a few days later that Pennsylvania Reported 2 More Novel Flu Cases.
All three cases in Pennsylvania were linked to the Washington County Agricultural Fair during the week of Aug. 13-20, 2011.
On September 9th, 2011 the CDC updated their SOIV (Swine Origin Influenza Virus) page (see CDC Update On Recent Novel Swine Flu Cases), acknowledging the possibility that limited human-to-human transmission of this trH3N2 virus might be occurring.
The CDC’s MMWR on November 23rd detailed the Iowa cases in a dispatch called Limited Human-to-Human Transmission of Novel Influenza A (H3N2) Virus — Iowa, November 2011.
By now, it was pretty apparent that this swine H3N2 virus had a greater affinity to human hosts than most of the other SOIVs we’d seen in the past (excluding the 2009 H1N1pdm virus).
Near the end of November the USDA reported they had detected a number of reassortant H3N2 viruses in swine, including 8 that displayed the 2009 H1N1 matrix (M) gene (see CIDRAP article New details emerge in novel H3N2 reports).
And in early December we learned that the CDC was Developing A trH3N2 Seed Vaccine . . . just in case this virus continued to spread.
December also saw a few more scattered cases in Minnesota and West Virginia, and the virus was given a new name WHO/FAO/OIE: Call It A(H3N2)v. By the end of the year, there were an even dozen cases reported around the country.
By April, 2012 a total of 13 human infections with this new strain had been detected in the United States. The summer of 2012 would see a major escalation in cases (more than 300), but for the next few months at least, the `first wave’ was over.
All of which serves as prelude to a series of articles that appear in a July Clinical Infectious Diseases Supplement (abstracts & excerpts available, full text behind a subscription / pay wall) called:
The Emergence of Influenza A (H3N2)v Virus: What We Learned From the First Wave, July 2011–April 2012
Volume 57 suppl 1 July 15, 2013
The Emergence of Influenza A (H3N2)v Virus: What We Learned From the First Wave
Clin Infect Dis. (2013) 57 (suppl 1): S1-S3 doi:10.1093/cid/cit324
Lyn Finelli and David L. Swerdlow
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Human Infections With Influenza A(H3N2) Variant Virus in the United States, 2011–2012
Clin Infect Dis. (2013) 57 (suppl 1): S4-S11 doi:10.1093/cid/cit272
Scott Epperson, Michael Jhung, Shawn Richards, Patricia Quinlisk, Lauren Ball, Mària Moll, Rachelle Boulton, Loretta Haddy, Matthew Biggerstaff, Lynnette Brammer, Susan Trock, Erin Burns, Thomas Gomez, Karen K. Wong, Jackie Katz, Stephen Lindstrom, Alexander Klimov, Joseph S. Bresee, Daniel B. Jernigan, Nancy Cox, Lyn Finelli, and for the Influenza A (H3N2)v Virus Investigation Team
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Estimates of the Number of Human Infections With Influenza A(H3N2) Variant Virus, United States, August 2011–April 2012
Clin Infect Dis. (2013) 57 (suppl 1): S12-S15 doi:10.1093/cid/cit273
Matthew Biggerstaff, Carrie Reed, Scott Epperson, Michael A. Jhung, Manoj Gambhir, Joseph S. Bresee, Daniel B. Jernigan, David L. Swerdlow, and Lyn Finelli
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Transmissibility of Variant Influenza From Swine to Humans: A Modeling Approach
Clin Infect Dis. (2013) 57 (suppl 1): S16-S22 doi:10.1093/cid/cit303
Karen K. Wong, Manoj Gambhir, Lyn Finelli, David L. Swerdlow, Stephen Ostroff, and Carrie Reed
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Multiple Contributory Factors to the Age Distribution of Disease Cases: A Modeling Study in the Context of Influenza A(H3N2v)
Clin Infect Dis. (2013) 57 (suppl 1): S23-S27 doi:10.1093/cid/cit298
Manoj Gambhir, David L. Swerdlow, Lyn Finelli, Maria D. Van Kerkhove, Matthew Biggerstaff, Simon Cauchemez, and Neil M. Ferguson
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In my next post, I’ll take a closer look at a couple of these reports.
