Standardization of terminology for the influenza virus variants infecting humans: Update

Joint announcement of FAO, OIE and WHO

30 January 2014

FAO, OIE and WHO continue working closely together to address influenza issues related to public health and animal health.

Over the past three to four decades, there have been multiple instances of sporadic transmission of influenza viruses between animals and humans. When influenza A(H3N2) viruses circulating in swine in the United States of America (USA) were detected in people in 2011, experts from WHO, FAO and OIE agreed that such viruses would be called H3N2 “variant” viruses (with a “v” placed after the subtype of the virus, e.g. H3N2v) in order to distinguish them from A(H3N2) human seasonal influenza viruses,1 which are antigenically and genetically different from each other. Other influenza viruses normally circulating in animals, e.g. avian influenza A(H5N1), A(H7N7), A(H7N9), and A(H9N2), which are found to sporadically infect people are simply called “avian influenza” or “zoonotic influenza” viruses 2.

This terminology has proven useful. Therefore, it was recently proposed that a similar terminology be adopted by WHO and partners to designate other non-seasonal influenza viruses of a subtype shared with human seasonal influenza viruses, particularly viruses of the H1N1, and H1N2 subtypes circulating in swine that are detected sporadically in humans. For example, a non-seasonal influenza A(H1N1) virus detected in a human would be denoted as A(H1N1)v and a non-seasonal influenza A(H1N2) virus detected in humans would be denoted as A(H1N2)v.

This would bring the terminology used by WHO, OIE, and FAO into alignment with that is being used widely, including by the United States Centers for Disease Control (US CDC)3.

Additional discussion on influenza virus terminology can be found at:

For more information, please contact FAO at, OIE at and WHO at