Scientists are keeping an eye on a new strain of flu virus in China that, while not yet causing sickness, has some potential to start another pandemic.

A new strain of the H1N1 virus, called G4 EA H1N1, has been detected among workers at hog farms and neighboring communities. A seven-year study in 10 Chinese provinces showed that 10.4% of hog farm workers, and 4.4% of others, tested positive for antibodies to G4 EA H1N1.

While the new virus has not yet caused any illness, researchers are concerned that it replicates in human airways as efficiently as other strains of H1N1.

“It’s a very important study, and the virus looks quite dangerous,” a Chinese researcher told the New York Times. “We need to be worried about any disease with the potential to spread human-to-human.”

The worry is that further change in the G4 EA H1N1 virus will increase its danger to human beings. The last time an H1N1 virus spread widely was in 2009, but the fatality rate was a relatively low 0.02%. By contrast, the most lethal pandemic in modern history, the 1918 outbreak, was caused by a virus with a fatality rate of 2.5%.