Reported Infections with Variant Influenza Viruses in the United States since 2005

When people are infected with influenza A viruses that are known to be genetically similar to viruses circulating in swine, these viruses are called “variant viruses” and denoted with a letter “v”. As of September 21, 2012, 345 cases of infection with variant influenza viruses have been reported in the United States since 2005. Of these 345 cases, 14 have been H1N1v viruses, 326 have been H3N2v viruses and 5 have been H1N2v viruses.

With the exception of one death, the remaining 344 people infected with variant viruses recovered from their illness. Most infections with variant viruses have occurred in children (persons 18 or younger) and most cases have reported direct or indirect exposure to swine prior to onset of illness. Limited transmission from close contact with an infected person has been observed in some investigations of human infections with variant viruses, but sustained human-to-human transmission has not been documented.

H3N2v

Beginning in August 2011, infection with an H3N2v virus was detected in a number of people across several U.S. states. More information about H3N2v is available at Influenza A (H3N2) Variant Virus Outbreaks.