A new World Health Organization report, set to be released on Tuesday, lists the coronavirus' possible origin scenarios in order of their likelihood.
According to the the Associated Press, which obtained a draft copy of the report, the most likely option is that the coronavirus jumped from bats to people via an intermediary animal host, perhaps at a wildlife farm in China. Next on the likelihood ranking is the possibility that the virus jumped directly from bats to people.
The report is the product of a month-long investigation by an international team that was sent to Wuhan, China, in January to investigate how the virus got into the human population, and from where. The effort, however, yielded few definitive answers.
The WHO team also evaluated less plausible theories, the AP reported, including that the virus might have spread to humans via frozen food products; the report authors deemed this scenario "not likely." One hypothesis was labeled "extremely unlikely" and all but dismissed: the possibility that the coronavirus escaped from a Chinese lab.
Chinese wildlife farms are a possible origin site
The WHO experts behind the report — which the AP got from a diplomat in Geneva, Switzerland — worked together with Chinese scientists during their trip. The WHO team said it got unfettered access to key places in Wuhan over four weeks, including hospitals, laboratories, and the Huanan Seafood Wholesale Market, where officials reported the first known cluster of COVID-19 cases in December 2019.
The group's conclusion, though far from certain, is that wildlife farms in southern China are the most likely place where the virus made a cross-species hop into humans.
"They take exotic animals, like civets, porcupines, pangolins, raccoon dogs, and bamboo rats, and they breed them in captivity," Peter Daszak, a disease ecologist and member of the WHO team, told NPR. He added that China shut down those wildlife farms in February 2020.
The coronavirus probably came into our population via one of those bred animals, perhaps a pangolin, rabbit, or ferret, according to the WHO. Daszak said his team found evidence that these wildlife farms supplied vendors at the Huanan market.
The virus likely came from bats, and it didn't leak from a lab
Although the WHO report does not pinpoint exactly where the coronavirus outbreak began, it does offer reasons why it almost certainly did not leak from a lab, as some unsubstantiated theories suggest.
Ideas about a lab leak often point to the Wuhan Institute of Virology, where some scientists were studying various coronaviruses prior to the pandemic. The lab is about 8 miles from the Huanan Seafood Wholesale Market.
But the WHO team found no evidence that samples of the new coronavirus existed at the institute, or at any other labs in China, before the pandemic began. The team also spoke with managers and staff at the institute about their safety protocols.
According to Peter Ben Embarek, a WHO scientist specializing in animal disease, it is "very unlikely that anything could escape from such a place."
Much more likely, the WHO experts said, is that the virus started circulating in bats first.
A study from February 2020 found that the new coronavirus shares 96% of its genetic code with a coronavirus seen in Chinese bat populations. Then another study revealed an even closer match: a 97.1% similarity to a coronavirus called RmYN02, which was found in bats in China's Yunnan province between May and October 2019.
Bats are common virus hosts — cross-species hops from bat populations also led to the outbreaks of Ebola, SARS, and the Nipah virus.
'Real concerns about the methodology'
Doubts about the trustworthiness of the WHO report linger, however. The AP revealed in December that the Chinese government was strictly controlling all research into the virus' origins, while simultaneously promoting theories that it came from outside of China. Mounting evidence also suggests that the virus was circulating in China months before the first cases were reported.
"We've got real concerns about the methodology and the process that went into that report, including the fact that the government in Beijing apparently helped to write it," US Secretary of State Antony Blinken told CNN on Thursday. During his confirmation hearing in January, Blinken said he thought China had misled the world about the coronavirus.
Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said he's reserving judgment about the WHO findings until he can "get a feel for what they had or did not have access to."
"Once I get that information, I'll be able to more adequately answer whether I trust it or not," Fauci said of the report in a White House press briefing on Monday.
The lingering uncertainty leaves a door open for unsubstantiated theories to continue to spread. Robert Redfield, who was head of the Centers for Disease Control and Prevention under President Donald Trump, recently reiterated one such idea: that the virus escaped from a Wuhan lab.
"Other people don't believe that. That's fine. Science will eventually figure it out," Redfield told CNN on Friday, adding, "I'm allowed to have opinions now."