Swine influenza in humans
Most swine influenza viruses (SIVs) do not cause disease in humans. However, some countries have reported cases of human infection with SIVs. Most of these human infections have been mild and the viruses have not spread further to other people. The H1N1 virus that caused the influenza pandemic in 2009-2010, thought to have originated in swine, is an example of an SIV that was able to spread easily among people and also cause disease.
Because pigs can become infected with influenza viruses from a variety of different hosts (such as birds and humans), they can act as a "mixing vessel," facilitating the reassortment of influenza genes from different viruses and creating a "new" influenza virus. The concern is that such "new" reassortant viruses may be more easily spread from person to person, or may cause more severe disease in humans than the original viruses. WHO and animal health sector partners are working at the human-animal interface to identify and reduce animal health and public health risks within national contexts.