Researchers behind a new study have concluded the "early epicentre" of the Covid-19 pandemic is "overwhelmingly" likely to be the highly-scrutinised Huanan seafood market despite prolonged speculation surrounding the nearby Wuhan Institute of Virology.
Theories the virus emerged from a covered-up laboratory leak were only fuelled when the World Health Organisation said last year investigations into the claim were inadequate.
It's a claim that has enraged Beijing, as China faces continued criticism over its early handling of the pandemic and accusations of withholding key information and data surrounding the first reported cases.
While the the peer-reviewed study, which was released on Tuesday after a preprint was shared earlier this year, doesn't disprove the lab leak theory, co-author Kristian Andersen believes it provides strong evidence the Huanan market was responsible for the pandemic.
Researchers mapped reports of cases to perform a spacial and environmental analysis and found early cases lived near to and centred on the market.
"The clustering is very, very specific," Mr Andersen, a professor in the Department of Immunology and Microbiology at Scripps Research, said.
Even cases that weren't directly linked to the market were found to live in close proximity of the market, co-author Michael Worobey, Professor and Head of Ecology and Evolutionary Biology at the University of Arizona, said.
"This is a clear indication that they were infected as the virus moved from the market into the local community surrounding the market," he explained.
'Huanan market would be the bullseye'
Commenting on one graphic from the study displaying virus centre points, co-author Dr Angela Rasmussen said: "If this were a dartboard, Huanan market would be the bullseye."
A second study the group has also published included "strong evidence" there were at least two introductions of Covid-19 into humans from zoonotic spillovers, with the first likely happening on November 18.
It also says circulation of the virus in humans prior to November 2019 was unlikely.
"We report that live SARS-CoV-2 susceptible mammals were sold at the market in late 2019 and, within the market, SARS-CoV-2-positive environmental samples were spatially associated with vendors selling live mammals," the study says.
However biologist Matt Ridley, co-author of Viral: The Search For The Origin of Covid-19, labelled the research as a "damp squib" in The Spectator, suggesting the studies brought little new to the table and lacked conclusive evidence.
He said scientists in virology feared to entertain the lab leak theory due to the damage it could do to their industry, adding Wuhan's "most intensive programme of research on SARS-like viruses in the world" could not be dismissed and warranted further investigation.
While Dr Rasmussen admitted the data is "incomplete and imperfect", "it overwhelmingly shows that the pandemic began at Huanan through zoonosis, not at the Wuhan Institute of Virology or any other lab".
"The evidence has stacked up for zoonosis. There remains no evidence for lab leak besides "started in Wuhan."
This shows the center points of Wuhan population density & Dec cases regardless of market association or not & virus lineage. The virus center points are all strongly linked to the market, while population is not.
If this were a dartboard, Huanan market would be the bullseye. pic.twitter.com/GUQkKwjwx3
— Dr. Angela Rasmussen (@angie_rasmussen) July 26, 2022
Wuhan back in lockdown
The studies were not the only reason the city where the virus first began to spread was making headlines, after the detection of four asymptomatic Covid-19 cases were detected.
It prompted authorities to shut down a district housing roughly one million people as China's unrelenting Covid-zero strategy rolls on.
Wuhan's district of Jiangxia, with over 900,000 residents, said its main urban areas must enter a three-day restriction from Wednesday, during which it will ban many large group events and dining at restaurants, close various public entertainment venues, agricultural product marketplaces and small clinics and suspend bus and subway services.
It also urged residents not to leave the area during the three days and encouraged travellers to avoid entry.
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