The bird flu virus H3N2 is endemic in pigs in China. It has recently been found in pigs in Vietnam. Specialists also think that this might lead to new variations of the influenza virus. Pigs can carry human influenza viruses. These viruses can combine in new ways, and exchange certain genes with H5N1. Through mutation, this would create a form of the virus that can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift. In August 2004, researchers in China found H5N1 in pigs.