When the investigators inoculated ferrets with 2009 H1N1 virus plus either seasonal H1N1 virus or seasonal H3N2 virus, the animals became co-infected with both viruses. However, only the 2009 H1N1 virus was then transmitted from co-infected ferrets to uninfected ferrets; there was no evidence that either of the seasonal flu viruses were transmitted between co-infected and uninfected animals. "The H1N1 pandemic virus has a clear biological advantage over the two main seasonal flu strains and all the makings of a virus fully adapted to humans," says Dr. Perez.

Next, the team conducted experiments to learn whether 2009 H1N1 virus would combine with seasonal flu viruses in co-infected animals to create new reassortant viruses. Some scientists have speculated that reassortant viruses may be more virulent or transmissible than either 2009 H1N1 or seasonal flu viruses alone. The researchers collected virus-containing material from the ferrets' nasal cavities, but found no evidence of reassortment between the 2009 H1N1 and seasonal influenza strains, either in ferrets that were directly infected with both viruses or in ferrets that came in contact with the co-infected animals.

Source: NIH/National Institute of Allergy and Infectious Diseases