The SARS-CoV-2 virus was unlikely to have leaked from a laboratory in Wuhan and the evidence pointed to natural origins, according to a World Health Organisation (WHO) and China joint expert team that concluded a visit to Wuhan, where the COVID-19 pandemic began.
The team also concluded there was no indication of the virus being spread among the population there prior to December 2019, when Wuhan’s hospitals first began reporting a pneumonia outbreak. The authorities confirmed human-to-human transmission in mid-January.
“Our initial findings suggest that the introduction through an intermediary host species is the most likely pathway and one that will require more studies and more specific, targeted research,” WHO scientist Peter Ben Embarek who led the international team, told reporters on Tuesday. The team of 17 international experts and 17 Chinese scientists had spent the past two weeks visiting hospitals, a seafood market that was one of the earliest clusters, and laboratories in Wuhan.
The location of the Wuhan Institute of Virology (WIV) in the city had led to theories suggesting the virus may have leaked from a lab, but Mr. Embarek said “the findings suggest that the laboratory incidents hypothesis is extremely unlikely to explain the introduction of the virus to the human population”.
The team examined four pathways: direct transmission from wildlife, transmission through intermediate hosts, transmission via cold chain products such as imported seafood, and a lab leak.
China’s officials have been strongly pushing back against the lab leak theory, while recently also suggesting the virus may have come to China via cold chain products from outside the country, a prospect that is being examined but also considered unlikely. The team studied all four possibilities including the lab leak.
Reports from Wuhan said the team spent around an hour at the market and four hours at the Wuhan Institute of Virology, and met with scientists there included China’s leading bat coronavirus expert, Shi Zhengli, who has been researching bat coronaviruses in the lab. There was no evidence that SARS-CoV-2 was being studied at any of the city’s labs, the team said.
Mr. Embarek’s comments suggested transmission through an intermediate host was the most likely scenario and the evidence pointed “towards natural reservoirs of the virus” considering similar viruses in the bat population.
“Since Wuhan is not a city or environment close to bat environments, a direct jump from bats to the city of wuhan is not very likely,” he said. “Therefore, we have tried to find what other animal species were introduced and moving in and out of the city that could have potentially introduced the virus, in particular at the Huanan seafood market”, the site of the first major cluster.
While so far the intermediate host has not been identified, samples of some animals known to be susceptible to coronaviruses were identified at the market and some of those traced back to farms or parts of China that harboured bat environments.
“The joint team in their study have identified the vendors who were trading these type of products, the suppliers of these vendors, the farms from where the products were coming from,” Mr. Embarek said.
Liang Wannian, head of the China team of experts, said there was no indication the virus was being spread in the population before December 2019. He also said there was no evidence to suggest the Huanan market was the source, as the earliest case in Wuhan, reported on December 8, 2019, was not linked to the market.