More Information on Viruses Combining

In experiments in Maryland (USA), researchers co-infected ferrets with the pandemic H1N1 virus and either a seasonal H1N1 virus or a seasonal H3N2 virus.

The H1N1 pandemic virus had a clear biological advantage over the two main seasonal flu strains and the makings of a virus fully adapted to humans. It is thought that the pandemic virus is more infectious, simply because it is new, so hosts haven't had a chance to build immunity yet. The older strains encounter resistance from the hosts' immunity to them.

The studies also confirmed findings by other researchers that the swine flu virus is able to grow deeper into the victim's lungs, allowing it to cause viral pneumonia. That may be why some victims with underlying medical conditions are more likely to develop severe illness from infections. They also found that the virus can in some cases grow in the animals' intestines as well. Reports in humans have shown that swine flu causes a higher incidence of diarrhea and gastrointestinal distress than seasonal flu.

The highly infectious nature of the swine flu virus underscores the need for vaccination against both seasonal influenza and the 2009 H1N1 influenza this fall and winter.