A bird flu virus commonly found in chickens in Hong Kong’s markets could mutate and jump more easily to humans, possibly leading to the next influenza pandemic, scientists said on Tuesday.

Researchers found the H9N2 virus in about two percent of chickens in a study between 2001 and 2003.

“H9N2 is widely circulating in this geographical region, and that increases the chance of this virus jumping to other species and degenerating into a novel subtype of influenza that is able to infect humans,” said Leo Poon, a microbiologist at the University of Hong Kong.

“Eventually, we will have a new pandemic strain. We don’t know when, we don’t know where, but better surveillance could help delay this disaster from happening,” he said. Poon was part of a team that conducted the study.

The H9N2 virus is different from the H5N1 strain that swept large parts of Asia earlier this year, killing 24 people. About 100 million poultry died or were culled.

H9N2 has been detected in pigs and at least three people since 1999 in Hong Kong. It has a lower mortality rate than H5N1, but that means there is also a greater likelihood of it passing between species and mutating into something deadlier.

“Most of the infected chickens don’t die, which means it can jump more easily to pigs, which are mixing vessels (for viruses) to mix and mutate,” Poon said.

“And if it mutates and jumps to humans, it will be more virulent,” he added.

Pigs are susceptible to a variety of flu viruses and can be infected with viruses from different species, such as ducks and humans, at the same time. If this happens, it is possible for the genes of these viruses to mix and create a new virus that can be deadly to humans.

Scientists say major flu pandemics occur every 30-35 years. The deadliest in the past century was the Spanish Flu pandemic of 1918-19 that killed between 20 million and 50 million people worldwide, including 500,000 in the United States.

The exact source of this virulent strain is unknown but is thought to have been wild birds.

The virus behind the last major flu outbreak, the Hong Kong Flu pandemic of 1968, is thought to have originated in wild aquatic birds such as ducks.