Flu viruses found among pigs in China appear able to spread in humans and have the potential to cause a pandemic, researchers say.

Authors of a study published online recently in the Proceedings of the National Academy of Sciences of the United States of Americawrote their finding suggests "immediate action is needed to prevent the efficient transmission" of such viruses to humans.

"Based on our data, I think that the public should know the risk," says Yoshihiro Kawaoka, a study author and professor in the division of virology at the University of Tokyo.

Though vaccines to prevent flu in pigs exist, authors of the report say they generally aren't used in China, which produces the world's largest supply of pork.

Most people would not be protected if exposed to two subtypes of the swine flu lineage known as Eurasian avian-like H1N1 – or EAH1N1 – that were highlighted by the researchers, and Kawaoka says it's difficult to determine how widespread the virus strains could become if they spread to humans.

The last time a different strain of swine flu – H1N1 – hit the U.S. at pandemic proportions, it infected nearly 61 million people, killing 12,469 from April 2009 to April 2010, according toestimates from the Centers for Disease Control and Prevention.

This year's flu vaccine protects against H1N1, but not the viruses focused on in the prceedings paper. Earlier in December, 2015, the CDC reported that about 40 percent of adults and children had received the flu vaccine as of Nov. 5.

"Seasonal flu vaccines are not designed to protect against swine influenza viruses," says Dr. Joe Bresee, chief of the epidemiology and prevention branch in the CDC's Influenza Division.

To conduct the study, scientists isolated 228 flu viruses from 36,417 pigs at slaughterhouses and farms in China, and sequenced the genomes of a representative sample of those belonging to the EAH1N1 lineage. They additionally tested viruses among ferrets to see whether they could spread through the air via respiratory droplets – such as from a sneeze or cough – with nine out of 10 tested EAH1N1 viruses proving capable of doing so.

EAH1N1 viruses have been circulating in pigs since 1979 and have caused some human infections, but now hold the potential of greater danger.

"After long-term evolution in pigs, the EAH1N1 [viruses] have obtained the traits to cause a human influenza pandemic," the study said.

The viruses also came in two subgroups, with only 3.6 percent of children age 10 or under and 13.4 percent of adults 60 and over possessing neutralization antibodies against the first subgroup. No younger adults had the protective antibodies, and no one in those age ranges possessed them for the other virus subgroup.

A spokesman from Hong Kong's health department told the South China Morning Post officials were aware of the study and would continue to monitor new flu developments.

Kawaoka says countries could take action by ramping up surveillance to identify where the viruses are and to warn the public to keep their distance from pigs.

Just like with other forms of the flu, swine flu viruses change constantly. When pigs get the flu, they show signs of illness similar to those exhibited by humans, such as fever, discharge from the nose and difficulty breathing. The flu typically isn't deadlyin pigs, according to the CDC, and it rarely spreads to humans, though in recent years two variants of swine flu other than H1N1 have hit people in the U.S. Farmers are more at risk of getting the virus than meat processors, Kawaoka says.

Even in the absence of a truly global pandemic, swine flu has been killing people. Deaths from an outbreak that has hit 1,190 people in Iran now total 112, according to Agence France-Presse. Cases also have been seen in Israel and India.

Source: U.S. News & World Report