Eric Feigl-Ding, an epidemiologist at Harvard University in the US, who is unrelated to the study, tweeted that the virus is just in pigs for now.
"Only two cases. And it's an older 2016 origin virus. No human to human yet. 10 per cent of swine farmers have antibodies. No real flashing red light evidence yet," he mentioned on the micro-blogging platfrom.
Despite five years of extensive exposure of humans to the virus, there's no evidence of it spreading from one person to another, said Carl T. Bergstrom, a biologist at the University of Washington in the US, who is unrelated to the study.
"There's no evidence that G4 is circulating in humans, despite five years of extensive exposure. That's the key context to keep in mind," Bergstrom tweeted.
However, he said it is important to monitor the emerging situation.
"What the paper does do is something important for the epidemiological community: it points to a virus that we need to be keeping a careful eye on," Bergstrom said.
"Screening will be important, particularly if clusters of illness emerge in swine workers," he said on Twitter.
The PNAS study demonstrated that the newly identified virus can efficiently infect ferrets via aerosol transmission, causing severe clinical symptoms in them like sneezing, wheezing, coughing, and a mean maximum weight loss ranging from 7.3 to 9.8 per cent of the mammals' body mass.
The study also noted that humans are not protected from the G4 virus by the immunity offered by other human influenza vaccine strains, indicating that there is no preexisting population immunity to the virus.
Blood sample analysis of workers in the swine industry indicated that nearly 10.4 per cent (35/338) of them were positive for the G4 flu virus.
Participants between 18 and 35 years of age had about 20 per cent positive rates of the virus in their blood, according to the study, indicating that the predominant G4 strain has acquired increased human infectivity.
"Such infectivity greatly enhances the opportunity for virus adaptation in humans and raises concerns for the possible generation of pandemic viruses," the scientists wrote in the study.
They said the newly identified virus is a growing problem in pig farms, adding that the widespread circulation of G4 viruses in pigs "inevitably increases their exposure to humans."
The scientists said two recent cases of G4 virus infection, reported in 2016 and 2019, were of a 46- and a nine-year-old, respectively.
According to the study, the two patients had neighbours who reared pigs, suggesting that G4 virus "could transmit from swine to human, and lead to severe infection and even death."
"Thus, it is necessary to strengthen the surveillance effort of G4 EA viruses
among swine and human populations," the researchers wrote in the study.
According to Bergstrom, the G4 virus may have to undergo some evolutionary change to spread readily in people, "and it may never do that."
"If it does? We know how to make vaccines for influenza viruses. It could be included in the seasonal vaccine, the only issue is timing." he noted on Twitter.