ABOVE: Wuhan, China

Investigators from the World Health Organization on a mission in China to track down the roots of the COVID-19 pandemic report that the prevailing hypothesis—that SARS-CoV-2 originated in an animal host and worked its way, possibly through intermediate hosts, to humans—is supported by their evidence. 

An alternative proposal that the virus came from a lab is “extremely unlikely,” Peter Ben Embarek, the WHO’s food safety and animal disease specialist and chair of the investigative team, tells The Guardian. It “isn’t a hypothesis we suggest implies further study. . . . There had been no publication or research of this virus or one close to this virus, anywhere in the world.”

See “Theory that Coronavirus Escaped from a Lab Lacks Evidence

For nearly a month, Embarek’s team has been in Wuhan, China, where COVID-19 was first noticed in late 2019. The Huanan Seafood Market in Wuhan had been identified as a common factor in the early cases, and the WHO group found animals sold there that have the potential to carry SARS-CoV-2 and that come from farms located in regions where bats harbor coronavirus relatives, virologist Marion Koopmans of the WHO team tells the Associated Press.

“The possible path from whatever original animal species all the way through to the Huanan market could have taken a very long and convoluted path involving also movements across borders,” Embarek told reporters at a press conference, Reuters reports. It’s also possible that frozen foods contaminated with the virus ushered SARS-CoV-2 into the human population, but Embarek said it’s not clear if virus on frozen products could lead to human infections.

Liang Wannian, who leads China’s team investigating the outbreak, said at the press briefing that COVID-19 cases were detected in late 2019 that weren’t connected to the seafood market, but no substantial outbreaks were going on elsewhere. “We haven’t been able to fully do the research, but there is no indication there were clusters before what we saw happen in the later part of December in Wuhan,” Liang told reporters.

According to The Guardian, Liang says the WHO’s digging will continue, while China’s investigation into COVID-19’s origins is complete.