Vaccines against African swine fever being tested in Vietnam are close to approval, global and U.S. veterinary officials said, in what would be a major breakthrough to tackle the deadly animal disease that regularly ravages pig farms worldwide.

African swine fever has for years disrupted the $250 billion global pork market. In the worst outbreak in 2018-19, about half the domestic pig population died in China, the world’s biggest producer, causing losses estimated at over $100 billion.

After decades of failed attempts due to the complexity of the virus, two vaccines co-developed by U.S. scientists being tested in large pilot schemes by Vietnamese companies are showing “very promising” results, Gregorio Torres, head of the science department at the World Organisation for Animal Health (WOAH), told Reuters in a telephone interview.

“We have never been so close to get a vaccine that may work,” Torres said, noting the two shots had “probably the highest chances to succeed” and be authorised for sale worldwide.