A draft version of the study, which was obtained by the Associated Press, also concludes that it is “extremely unlikely” the virus was leaked from a laboratory in the Chinese city of Wuhan, where Covid-19 first emerged in late 2019.
It had been claimed that scientists at the Wuhan Institute of Virology (WIV) were experimenting with a virus genetically similar to Sars-CoV-2 before it was leaked into the community.
The report, which has yet to be publicly released, is based largely on a visit by a WHO team of international experts and scientists to Wuhan from mid-January to mid-February.
According to the group’s findings, evidence suggests Sars-CoV-2 emerged naturally in bats before passing to humans via an unconfirmed intermediary animal host – a scenario deemed “likely to very likely” by the scientists.
The closest relative of the Covid-19 virus has been found in bats, which carry a wide variety of coronaviruses. However, the report says that “the evolutionary distance between these bat viruses and Sars-CoV-2 is estimated to be several decades, suggesting a missing link”.
It said that highly similar viruses have been found in pangolins, but also noted that mink and cats are susceptible to the Covid virus, raising the possibility that these animals could be carriers.
The WHO scientists, who were working alongside Chinese health officials, highlighted other scenarios in which Covid-19 could have emerged.
They evaluated direct spread from bats to humans as “likely”, and said that spread through cold-chain food products was “possible”.
The market was an early suspect because some stalls sold a range of animals, and some people wondered whether they had brought the new virus to Wuhan. The report noted that a range of animal products, ranging from bamboo rats to deer, often frozen, were sold at the market, as were live crocodiles.
Last month, Professor Liang Wannian, head of the Chinese envoy working on the WHO investigation, said the virus could survive for long periods at refrigerated temperatures and may have been introduced to the Wuhan seafood market via frozen goods – a theory advocated by China.
However, he said that the first detected case of Covid-19 in Wuhan had no link to the market, indicating that it may not have been responsible for the city’s earliest outbreak.
On the possibility of a laboratory leak, the WHO report says this is “an extremely unlikely pathway”.
The WHO closely inspected the Institute of Virology last month, concluding “it was very unlikely that anything could escape from such a place”.
The authors of the study call for further investigations into the different hypotheses on the origins of Covid-19, except the lab leak theory.
The report’s release has been repeatedly delayed, raising questions about whether Chinese officials were trying to skew the conclusions to prevent blame for the pandemic falling on China.
However, its failure to pinpoint a definitive cause for the outbreak of Covid-19 is not unexpected, and means the search for the origins of the virus is likely to continue for years to come.
Already, the study has drawn criticism from US secretary of state Antony Blinken, who said America had concerns about the “methodology and the process” of the report, including that the Chinese government “apparently helped to write it”.
While there needs to be “accountability for the past”, the focus should be on building a stronger system for the future, he said on CNN.
Anthony Fauci, the top Covid-19 adviser to president Joe Biden, said he did not know whether the report would be a whitewash.
“What I would like to do is first see the report,” he said. “You’re getting a lot of conjecture around about what they did and what they were allowed to do or not.
“If, in fact, obviously, there was a lot of restrictions on the ability of the people who went there to really take a look, then I’m going to have some considerable concern about that.”