Influenza A (H3N2) Variant Virus

Influenza viruses that normally circulate in pigs are called “variant” viruses when they are found in people. Influenza A H3N2 variant viruses (also known as “H3N2v” viruses) with the matrix (M) gene from the 2009 H1N1 pandemic virus were first detected in people in July 2011. The viruses were first identified in U.S. pigs in 2010. During 2011, 12 human infections with H3N2v were detected. During 2012, there were multiple outbreaks of H3N2v resulting in 309 reported cases. Sporadic infections with H3N2v have continued to be detected since that time. Infections with H3N2v have mostly been associated with prolonged exposure to pigs at agricultural fairs. Limited human-to-human spread of this virus has been detected in the past as well but no sustained or community spread of H3N2v has been identified at this time. It’s possible that sporadic infections and even localized outbreaks among people with this virus will continue to occur. TheCenters for Disease Control and Prevention (CDC) continues to monitor this situation closely and will report cases of H3N2v and other variant influenza viruses weekly inviruses weekly in FluView.