Science's COVID-19 reporting is supported by the Heising-Simons Foundation.
Where SARS-CoV-2 came from before it began its 15-month rampage around the globe is the biggest pandemic puzzle of all.
Repeated delays in the report's release raised questions about whether the Chinese side was trying to influence the findings.
Produced by an global team of scientists after a carefully negotiated visit to China, where COVID-19 was first recognized, the report concludes that the likeliest start of the pandemic was a bat coronavirus that infected another, unidentified animal and then moved on to humans.
That's always been the favored hypothesis of many virologists, but the team convened by the World Health Organization (WHO) reports little fresh evidence to support it, and members acknowledge several other scenarios, including an accidental release from a lab, remain possible. The report does, however, lay out plenty of next steps. WHO Director-General Tedros Adhanom Ghebreyesus said on Monday all hypotheses are on the table and warrant complete and further studies.
The WHO team had arrived in Wuhan, China to probe Sars-CoV-2 origins in January 2021.
The team concluded the virus was most likely to have been passed from bats via an "intermediate animal host" to humans before sparking an "explosive outbreak" in Wuhan in December 2019. But most health experts have said it is unlikely the new coronavirus came from a lab or was engineered by humans.
The WHO team's leader, Peter Ben Embarek, told a press briefing it was "perfectly possible" the virus had been circulating in November or October 2019 around Wuhan, and so potentially spreading overseas earlier than documented so far.
That's understandable, some researchers say.
Rasmussen agrees. "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", she says. He made his remarks to member countries before a press conference coinciding with the publication of the report. However, the World Health Organization report says "the evolutionary distance between these bat viruses and (the coronavirus) is estimated to be several decades, suggesting a missing link".
Which animal could have spread the virus to humans?
What are the most likely scenarios?
Spillover via frozen meat from an infected animal, a route the team labeled as "possible". The WHO-backed team considered the scenario but concluded it "extremely unlikely" and devoted only a comparatively small space in the final report to the idea of an accidental laboratory leak. "And in a compromise, you have to respect the other's views". While it is possible an infected animal contaminated the packaging and was brought to Wuhan which then infected humans, the report said the probability is very low. "At this point, it may well have disappeared from any intermediate host, so sampling bats, in particular, is probably the most likely to yield results".
Dominic Dwyer, an Australian expert on the mission, said he was satisfied there was "no obvious evidence" of a problem at the Wuhan Institute of Virology.
It was a year ago, as the virus cases grew in the US, that former US President Donald Trump opened a front against China claiming that the virus leaked from Wuhan's lab. It was conducted by a team made up of both worldwide and Chinese experts. The first case was a 62-year-old man who developed symptoms on 1 December 2019.
What about the Huanan market? "We did not reach 100% agreement to discard these cases". It found only 28 percent of confirmed early cases had exposure only to the Huanan market, while a further 4.8 percent had exposure to the market as well as other markets. Tedros recommended a full analysis of the trade in animals and products in markets across Wuhan, particularly those linked to early human cases.
The market was identified early in the pandemic as a likely incubator of SARS-CoV-2, resembling the spawning in Guangdong province in 2002 of severe acute respiratory syndrome (SARS) - a bat-borne coronavirus that spread to civets and raccoon dogs before killing about 800 people.