Influenza A(H3N2)v Virus in Humans

In the United States, in contrast to the 309 cases reported in 2012, only 19 cases of human infection with a non-seasonal variant of Influenza A(H3N2) viruses were reported in 2013. This particular virus was designated Influenza A(H3N2)v37 and was known to have been circulating in swine.

One virus originating from a human case with onset in 2013 has been fully characterized and is almost identical to Influenza A(H3N2)v viruses isolated from patients in the USA in 2012. In 2013, only 1 person was hospitalized as a result of Influenza A(H3N2)v virus infection and there were no deaths[1].

[Chart by Fred de Vries]

The majority of human cases with influenza A(H3N2)v virus infections have occurred in children and are generally mild and associated with exposure to swine,[2] especially among participants in agricultural fairs during the northern hemisphere’s summer and early autumn months.

A variety of influenza A(H3N2) virus strains are endemic in swine populations in most regions of the world. Depending on geographic location, the genetic and antigenic characteristics of these viruses differ. Human infections with non-seasonal influenza A(H3N2) viruses have been documented in Asia, Europe and North America.[3]

[1] http://www.cdc.gov/flu/swineflu/h3n2v-case-count.htm.
[2] http://www.cdc.gov/flu/swineflu/h3n2v-basics.htm#what-is.
[3] Myers et al: Cases of swine influenza in humans: a review of the literature in Clinical Infectious Diseases - 2007