- After an investigation, the WHO said it's "extremely unlikely" the coronavirus leaked from a lab.
- But the WHO's director-general said its investigation of that theory wasn't "extensive enough."
- There's no evidence the virus had been in any labs, but the WHO couldn't conduct a full audit.
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After a month-long investigation in Wuhan, the World Health Organization has offered the most comprehensive analysis to date of where the coronavirus might have come from and how it could have gotten into the human population.
The WHO report, released Tuesday, lists the coronavirus' possible origin scenarios in order of their likelihood. At the top is the possibility that the coronavirus jumped from bats to people via an intermediary animal host, perhaps at a wildlife farm in China. Last on the ranking is the controversial theory that the virus leaked from a Chinese lab.
But in a press conference Tuesday, the WHO's director-general, Tedros Adhanom Ghebreyesus, said he does "not believe that this assessment was extensive enough."
"Although the team has concluded that a laboratory leak is the least likely hypothesis, this requires further investigation, potentially with additional missions involving specialist experts, which I am ready to deploy," he said. Tedros added that members of the international WHO team who traveled to China "expressed the difficulties they encountered in accessing raw data."
Following the report's release, the US and a dozen other countries have called for an independent investigation into the coronavirus' origins - one that would be "free from interference and undue influence," The Wall Street Journal reported.
A lab leak is 'extremely unlikely,' but the WHO didn't audit Wuhan labs
Tedros said the lab-leak hypothesis should "remain on the table," since the WHO experts spent only hours at each high-level biosafety lab in Wuhan.
Peter Ben Embarek, a WHO scientist specializing in animal disease, said during the press conference that the group didn't do "a full investigation or audit" of any particular lab. Overall, he added, the possibility of a lab leak "did not receive the same depth of attention and work" as other hypotheses about the virus' origin.
Still, the report offers compelling reasons why it's extremely unlikely the virus escaped from a lab.
The team found no evidence that samples of the new coronavirus existed at the Wuhan Institute of Virology, where scientists were studying various coronaviruses prior to the pandemic, before the first COVID-19 cases were reported in December 2019.
The WHO also didn't find any records indicating that viruses closely related to the new coronavirus were kept in any Chinese lab before that month. There were also no viruses that, when combined, could have produced the new coronavirus.
Additionally, none of the staff in any Wuhan labs studying coronaviruses reported cases of respiratory illnesses "during the weeks/months prior to December 2019," the report said.
Blood samples from staff during that time (which are taken routinely from biosafety lab workers to monitor their health) also all tested negative for coronavirus antibodies. This suggests no lab workers got infected prior to the pandemic.
'This is something coming out of our labs'
The WHO team's report did reveal, however, that the Wuhan Institute of Virology (WIV) moved to a new location in early December 2019. The new facility happened to be about 8 miles from the Huanan Seafood Wholesale Market, to which China's first cluster of cases was linked.
That proximity, coupled with the fact that there were multiple labs in Wuhan studying coronaviruses at the time the pandemic began, has led to speculation about a possible link between a lab and the market outbreak.
"Even the staff in these labs told us that was their first reaction when they heard about this new emerging disease, this coronavirus: 'This is something coming out of our labs,'" Embarek said.
"They all went back to their to their records and work to try to find out if there was a link but nobody could find any trace of something similar to this virus in in their records or their their samples," he added.
But Embarek's team didn't have the resources to fully verify that claim.
"A team of scientists is not qualified to conduct a detailed audit of WIV's records, or get access to institutional files, lab notebooks, databases, or freezer inventories," virologist Angela Rasmussen, a virologist and member of the WHO team, told Science.
Dominic Dwyer, a WHO microbiologist who's worked in high-level biosafety labs before, said on Tuesday that the team was "satisfied there was no obvious evidence of a problem," in any of the labs they visited. He noted as well that a complete forensic examination of a lab is a complex process, and that was "not what we were there to do."
The WHO team did, however, speak with managers and staff at the labs about their safety protocol, and confirmed the facilities were well-managed.
A wealth of evidence points to the conclusion that bats first passed the coronavirus to an animal, the WHO experts said. Then that animal population passed it along to humans. Indeed, a May study revealed that the new coronavirus shared 97.1% of its genetic code with 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.