WHO says 'most likely' pathway of Covid virus was from animals to humans, dismisses lab leak theory

• Liang Wannian, head of the expert Covid-19 panel at China's National Health Commission, said ongoing research into the origins of the virus must focus on how the virus circulated in animals before infecting humans.
• Scientists have been working in the Chinese city of Wuhan for the past four weeks as part of their search for clues to the origins of the Covid-19 pandemic.
• The team of investigators has visited hospitals, laboratories and markets, including the Huanan Seafood Market, the Wuhan Institute of Virology and the Wuhan Center for Disease Control laboratory.

An international team of scientists led by the World Health Organization said Tuesday that the search for how the coronavirus was first introduced remains a "work in progress," with further research needed into how and whether the disease circulated in animals before infecting humans.

Scientists have been working in the Chinese city of Wuhan, where the disease was first identified, for the past four weeks as part of their search for clues to the origins of the Covid-19 pandemic.

The team of investigators has visited hospitals, laboratories and markets, including the Huanan Seafood Market, the Wuhan Institute of Virology and the Wuhan Center for Disease Control laboratory.

The visit, which has been shrouded in secrecy, was also expected to see researchers speak with early responders as well as some of the first patients. The team completed two weeks of quarantine before beginning to visit local sites.

Dr. Peter Ben Embarek, the WHO's food safety and animal disease specialist and chairman of the investigation team, said at a press briefing that the "most likely" pathway for Covid was a crossover into humans from an intermediary species. This hypothesis will "require more studies and more specific (and) targeted research," he said.

The initial findings of the investigation did not find evidence of large Covid outbreaks in Wuhan or elsewhere before Dec. 2019. However, researchers did find evidence of wider Covid circulation outside the Huanan Seafood Market that same month, Ben Embarek said.

He added it was not yet possible to pinpoint the animal intermediary host for the coronavirus, describing the findings after nearly a month of meetings and site visits as "work in progress."

"In terms of understanding what happened in the early days of December 2019, did we change dramatically the picture we had beforehand? I don't think so," Ben Embarek said.

"Did we improve our understanding? Did we add details to that story? Absolutely," he said.

The WHO has sought to manage expectations of a definitive conclusion to the origins of the Covid pandemic. To put the mission in a broader context, it took more than a decade to find the origins of SARS, while the origins of Ebola — first identified in the 1970s — is still not yet known.

It is hoped that information of the earliest known cases of the coronavirus, first detected in Wuhan in late 2019, could help to identify how the outbreak started and prevent similar pandemics in the future.

After concerns about access and delays in obtaining visas, the World Health Organization-led team arrived in Wuhan on Jan. 14 to investigate the origin of the coronavirus alongside Chinese scientists.

Lab leak 'extremely unlikely'

A theory that the coronavirus was leaked from the Wuhan Institute of Virology was discredited by the team of investigators. The hypothesis had been perpetuated by former President Donald Trump's administration, without the weight of evidence, and strenuously denied by Chinese officials.

"The laboratory incident hypothesis is extremely unlikely to explain the introduction of the virus into the human population," Ben Embarek said. "Therefore, is not in the hypotheses that we will suggest for future studies."

Speaking alongside the WHO's Ben Embarek from the Hilton Optics Valley Hotel in Wuhan on Tuesday, Liang Wannian, head of the expert Covid panel at China's National Health Commission, said he agreed with this assessment.

The team had reached the conclusion that a lab leak should be regarded as extremely unlikely "on the basis of a serious discussion and very diligent research," he added.

Liang said ongoing research into the origins of the virus must focus on how the virus circulated in animals before infecting humans.

Animal hosts were yet to be identified but bats and pangolins are both potential candidates for transmission, Liang said, but samples from these species were not found to be "sufficiently similar" to the Covid virus.

The high susceptibility of minks and cats to the Covid virus indicates there may be other animals that serve as reservoirs, Liang continued, but research remains insufficient at present.

China's National Health Commission spokesperson said there could have been an unreported circulation of the coronavirus before it was first detected in Wuhan. However, Liang said there was no evidence of substantial Covid circulation in Wuhan before the late 2019 outbreak.

International concern

The WHO has previously cited genetic sequencing that showed the coronavirus had started in bats and likely jumped to another animal before infecting humans.

Many of the people that had fallen ill with the new virus in Wuhan, a city with a population of roughly 11 million, were reported to have had links to the Huanan Seafood Market.

Scientists initially suspected the virus came from wild animals sold at the seafood market, prompting China to swiftly restrict public access to the market at the beginning of last year.

China's CDC has since said samples taken from the seafood market suggest it was a place where the virus spread, not where the outbreak first emerged.

Further to this, China's Liang said on Tuesday that Huanan Seafood Market was one of the places where the coronavirus first emerged, but he added it was not possible with current evidence to determine how the virus was first introduced to the seafood market.

The origins of the coronavirus remain important because the virus is constantly evolving, as highly infectious mutant strains identified in the U.K. and South Africa demonstrate.

To date, more than 106 million people have contracted the coronavirus worldwide and it has caused at least 2.32 million deaths, according to data compiled by Johns Hopkins University.

The U.S., by far, has reported the highest number of confirmed Covid cases and deaths, with more than 27 million reported infections and 465,072 fatalities.

China has published little information on its research into the origins of the coronavirus and there had been widespread international concern about what the researchers in Wuhan will be allowed to see and do as part of their investigation.

— CNBC's Evelyn Cheng contributed to this report.

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