Researchers in China have discovered a strain of swine flu that is capable of triggering another pandemic.

A report published in peer-reviewed science journal Proceedings of the National Academy of Sciences earlier this week identified the G4 EA H1N1 strain of flu, which is genetically descended from the H1N1 strain that caused a pandemic in 2009.

It has “all the essential hallmarks of a candidate pandemic virus”, scientists at Chinese universities and China’s Center for Disease Control and Prevention said in the study.

Researchers took 30,000 nasal swabs from pigs between 2011 and 2018. A total of 179 swine flu viruses were isolated, the majority of which were a new kind that has been dominant among pigs since 2016.

Following various experiments, G4 was found to be highly infectious, replicating in human cells and causing more severe symptoms in ferrets than other viruses do.

Any immunity humans gain from exposure to seasonal flu does not protect against G4, tests also showed.

As many as 4.4 per cent of the general population appeared to have been exposed to the virus, therefore showing that it has passed from animals to humans. There is no evidence yet that the virus can be passed between humans.

“Controlling the prevailing G4 EA H1N1 viruses in pigs and close monitoring in human populations, especially the workers in swine industry, should be urgently implemented,” the study authors said.

The World Health Organisation will read the Chinese report carefully, spokesman Christian Lindmeier told a Geneva briefing on Tuesday.

“It … highlights we cannot let our guard down on influenza and need to be vigilant and continue surveillance even in the coronavirus pandemic,” he said.

There is no imminent threat of a new pandemic despite the virus’ capability to infect humans, said Carl Bergstrom, a biologist at the University of Washington.

“There’s no evidence that G4 is circulating in humans, despite five years of extensive exposure,” he said on Twitter. “That’s the key context to keep in mind.”

The new swine flu is still “in the stage of examination”, said Anthony Fauci, the director of the US National Institute of Allergy and Infectious Diseases.

It’s not “an immediate threat where you’re seeing infections, but it’s something we need to keep our eye on, just the way we did in 2009 with the emergence of the swine flu.”

This article originally appeared on Over60.