A strain of flu that has been circulating in pigs for decades is now capable of sickening humans and could cause to a pandemic similar to the one swine flu caused in 2009, a new study found.

A team of researchers from China and Japan recently found that a type of swine flu virus called EAH1N1 is now capable of sickening humans on a global scale, and published their discovery in the Proceedings of the National Academy of Sciences. The researchers wrote that the virus has been found in pigs since 1979, but “long-term evolution” in the animals have changed the virus and it’s now capable of not just making humans sick, but efficiently spreading between them.

The researchers warned EAH1N1 is now able “to cause a human influenza pandemic.” Their research indicated that several countries have already reported human cases of the illness.

The study “suggests that immediate action is needed” to prevent humans from getting the EAH1N1 virus, researchers wrote in the article’s summary, because of how it can spread and the fact that none of the humans they tested had developed antibodies for one particular flu strain.

The Centers for Disease Control and Prevention has estimated that the 2009 swine flu outbreak, caused by the different H1N1 virus, killed anywhere between 151,700 and 575,400 people.

The World Health Organization says pigs have been known to generate new flu viruses because they are capable of getting infected by several different animals and humans. The viruses blend together in pigs, creating new strains that can make humans sicker than the original viruses.