Researchers studying influenza in pigs have identified the strain G4 EA H1N1 that has infected 10% of swine workers in some areas of China. Testing of pigs across 10 provinces in China from 2011 to 2018 found that the new strain has some genetic similarity to the A H1N1 pdm09 strain which caused the last pandemic in 2009 -2010 and now circulates as a seasonal influenza. The researchers warn that since 2016, the G4 EA H1N1 has been the main strain in pigs. Twenty percent of swine workers aged 18 to 35 years old were positive for antibodies. This may mean that the "virus has acquired increased human infectivity".
Influenza viruses circulate in pigs and birds, and occasionally infect humans. They have the potential to cause a pandemic if they mutate to become easily transmissible from human to human. There are several known swine flus and bird flus, including H5N1 and H7N9, that show pandemic potential.