A joint World Health Organsiation (WHO)-China study on the origins of COVID-19 says that transmission of the virus from bats to humans through another animal is the most likely scenario and that a lab leak is “extremely unlikely”, the Associated Press (AP) reported on Monday (29 March).
The report is based largely on a visit by a WHO team of international experts to Wuhan, the Chinese city where COVID-19 was first detected, from mid-January to mid-February.
The findings were largely as expected and left many questions unanswered, but the report provided in-depth detail on the reasoning behind the team’s conclusions. The researchers proposed further research in every area except the lab leak hypothesis.
The report’s release has been repeatedly delayed, raising questions about whether the Chinese side was trying to skew the conclusions to prevent blame for the pandemic falling on China.
A WHO official said late last week that he expected it would be ready for release “in the next few days.”
The AP said it received what appeared to be a near-final version of the report on Monday but that it wasn’t clear whether the report might still be changed prior to its release.
The researchers listed four scenarios in order of likelihood for the emergence of the virus named SARS-CoV-2. Topping the list was transmission through a second animal, which they said was likely to very likely. They evaluated direct spread from bats to humans as likely, and said that spread through “cold-chain” food products was possible but not likely.
The closest relative of the virus that causes COVID-19 has been found in bats, which are known to carry 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 highly similar viruses have been found in pangolins, but also noted that mink and cats are susceptible to the COVID virus, which suggests they could be carriers.
Peter Ben Embarek, the WHO expert who led the Wuhan mission, said on Friday that the report had been finalized and was being fact-checked and translated.
“I expect that in the next few days, that whole process will be completed and we will be able to release it publicly,” he said.
The draft report is inconclusive on whether the outbreak started at a Wuhan seafood market that had one of the earliest clusters of cases in December 2019.
The discovery of other cases before the Huanan market outbreak suggests it may have started elsewhere. But the report notes there could have been milder cases that went undetected and that could be a link between the market and earlier cases.
“No firm conclusion therefore about the role of the Huanan market in the origin of the outbreak, or how the infection was introduced into the market, can currently be drawn,” the report says, according to the AP.
As the pandemic spread globally, China found samples of the virus on the packaging of frozen food coming into the country and, in some cases, have tracked localized outbreaks to them.
The report said that the cold chain, as it is known, can be a driver of long-distance virus spread but was sceptical it could have triggered the outbreak. The report says the risk is lower than through human-to-human respiratory infection:
“While there is some evidence for possible reintroduction of SARS-CoV-2 through handling of imported contaminated frozen products in China since the initial pandemic wave, this would be extraordinary in 2019 where the virus was not widely circulating.”