Researchers in China have found a new type of swine flu that is able to trigger a pandemic, according to a study published Monday in the U.S. science journal PNAS.
Christened G4, it is genetically descended from the H1N1 strain that caused a pandemic in 2009.
The authors called for urgent measures to monitor people working with pigs.
According to scientists at Chinese universities and China's Center for Disease Control and Prevention, the strain has "all the essential hallmarks of being highly adapted to infect humans."
Researchers took 30,000 nasal swabs from pigs in slaughterhouses in 10 Chinese provinces and in a veterinary hospital, allowing them to isolate 179 swine flu viruses, from 2011 to 2018.
G4 was observed to be highly infectious, replicating in human cells and causing more serious symptoms in ferrets than other viruses.
Tests revealed that any immunity humans gain from exposure to seasonal flu does not provide protection from G4.
According to blood tests, which showed antibodies created by exposure to the virus, 10.4% of swine workers had already been infected.
"It is of concern that human infection of G4 virus will further human adaptation and increase the risk of a human pandemic," researchers stated.