A new type of swine flu with the potential of triggering a pandemic has been discovered in China, a study published in the science journal Proceedings of the National Academy of Sciences on Monday said. It is genetically descended from the H1N1 strain and is named G4.

The World Health Organization had in 2009 declared H1N1 a pandemic. The symptoms include fever, chills and sore throat and the infection is similar to seasonal influenza. India has recorded a few hundred infections some years and many thousands in other years.

Scientists at Chinese universities and China’s Center for Disease Control and Prevention said G4 possesses “all the essential hallmarks of being highly adapted to infect humans”. Tests also showed that any immunity that humans gain from exposure to seasonal flu does not provide protection against G4.

Researchers carried out the study between 2011 and 2018 during which they took 30,000 nasal swabs from pigs in slaughterhouses and 1,000 more from a veterinary hospital in 10 Chinese provinces. The swabs collected yielded 179 swine influenza viruses. They found that the majority of the pigs were infected with the G4 strain of the H1N1 virus.

Experiments on ferrets revealed that G4 was highly infectious, replicating in human cells. Blood tests showed 10.4% of swine workers had already been infected. The authors called for urgent measures to monitor people working with pigs.

The virus has already passed from animals to humans as tests revealed that 4.4% of the general population appeared to have been exposed. However, there is no evidence yet that it can be passed from human to human. “It is of concern that human infection of G4 virus will further human adaptation and increase the risk of a human pandemic,” the researchers said, according to AFP.

James Wood, the head of the department of veterinary medicine at Cambridge University, said the study shows that humans are constantly at risk of new zoonotic pathogens. “…Farmed animals, with which humans have greater contact than with wildlife, may act as the source for important pandemic viruses,” he added.