China's Wuhan wet market may be the source of origin of Covid pandemic and not the Wuhan Institute of Virology (WIV) as previously speculated, a team of US scientists has revealed in two new studies.
The studies, not yet peer-reviewed, revealed that the SARS-CoV-2 was very likely present in live mammals sold in the Huanan Seafood Wholesale Market in late 2019.
Scientists, including those from the University of Arizona, also suggested that the virus twice spilled over into people working or shopping there, the New York Times reported.
However, the team said they found no support for an alternate theory that the coronavirus escaped from a laboratory in Wuhan.
"When you look at all of the evidence together, it's an extraordinarily clear picture that the pandemic started at the Huanan market," Michael Worobey, an evolutionary biologist at the University of Arizona and a co-author of both studies, was quoted as saying.
Earlier analysis also suggested that the first known case of the coronavirus was a vendor at the Huanan market.
But no wildlife was left at the market by the time Chinese researchers arrived in early 2020 to collect genetic samples, the report said.
The Huanan Seafood Wholesale Market was an early object of suspicion when Covid first swept across Wuhan and was also shut later.
But, the link to the market seemed to weaken as the coronavirus spread, and questions arose about the research carried out at the WIV, where scientists studied coronaviruses, the report said.
In the studies, Worobey and his colleagues estimated the latitude and longitude of 156 cases of Covid in Wuhan in December 2019. The highest density of cases centered around the market.
The researchers then mapped cases in January and February. They used data collected by Chinese researchers from Weibo, a social media app that created a channel for people with Covid to seek help.
The 737 cases drawn from Weibo were concentrated away from the market, in other parts of central Wuhan with high populations of elderly residents.
The patterns pointed to the market as the origin of the outbreak, the studies found, with the coronavirus then spreading to the surrounding neighbourhoods before moving out farther across the city.
The researchers ran tests that showed it was extremely unlikely that such a pattern could be produced merely by chance, the report said.
"It's very strong statistical evidence that this is no coincidence," Worobey said.