Chinese government scientists on Wednesday published a long-awaited study about a market in the city of Wuhan, acknowledging that animals susceptible to the coronavirus were there around the time the virus emerged. But the scientists also said that it remained unclear how the pandemic began.
The study, published in the journal Nature, focused on swabs taken from surfaces in early 2020 at the Huanan Seafood Wholesale Market, a large market where many of the earliest known Covid patients had worked or shopped. The Chinese scientists had posted an early version of their genetic analysis of those samples in February 2022, but at the time downplayed the possibility of animal infections at the market.
The scientists, many of whom are affiliated with the Chinese Center for Disease Control and Prevention, also wanted to publish their data in a peer-reviewed journal. And as part of that process, the scientists uploaded more genetic sequence data to a large international database, the administrators of the database said last month.
A few weeks after the data became public, a team of international scientists who had been studying the origins of the pandemic said they stumbled upon the sequences. They found that samples testing positive for the coronavirus contained genetic material belonging to animals, including large amounts that were a match for the raccoon dog, a fluffy mammal sold for fur and meat that was known to be able to spread the coronavirus.
That analysis, the subject of a report posted online in late March, did not prove that a raccoon dog itself was infected or that animals gave the virus to people. But it established that raccoon dogs deposited their genetic signatures in the same place where genetic material from the virus was left.
Many virologists said that scenario was consistent with one in which the virus spilled into people from an illegally traded wild animal at the market.
It appeared that the international team’s analysis sped up the release of the Chinese scientists’ study about the same data: The article appeared on Wednesday on Nature’s website with a note saying that it had been accepted for publication, but was still an “early version” and had not yet been edited.
Several authors of the article affiliated with the Chinese C.D.C., William J. Liu, George Gao and Guizhen Wu, did not respond to requests for comment.
In their first version of the article from February 2022, the Chinese authors did not mention finding any genetic material from raccoon dogs in the market swabs, which were taken from walls, floors, metal cages and carts. Beyond that, they said that the data did not point to any infected animals.
But in Wednesday’s version a little more than a year later, they wrote that the study “confirmed the existence of raccoon dogs” and other animals susceptible to the coronavirus at the market.
Many scientists believe that the existing evidence points to those animals likely acting as so-called intermediate hosts for the virus, which probably originated in bats. But they also say the evidence does not completely rule out a scenario in which people gave the virus to animals at the market.
The Chinese authors stressed that uncertainty in the new study. They also raised the notion that the virus could have been ferried to the Wuhan market on packages of frozen food, also known as cold chain products. Many scientists consider that scenario highly improbable, but China has promoted it because it gives credence to the idea that the pandemic could have started outside of the country and arrived via imported foods.
“The possibility of potential introduction of the virus to the market through infected humans, or cold chain products, cannot be ruled out yet,” the article said.
The study included several other unlikely findings as well, outside scientists said in interviews on Wednesday. For example, it said that the swabs contained genetic material from a number of animals that were almost certainly not present at the market, including pandas, chimpanzees and mole-rats.
Alice Hughes, an associate professor at the University of Hong Kong focused on conservation biology, said that the inclusion of those animals suggested either that the authors had incorrectly categorized the genetic material or that the samples were contaminated during sequencing in a lab.
“This paper’s greatest asset is the fact that it releases a data set for other scientists to analyze more carefully and responsibly,” Dr. Hughes said. “Given the glaring errors in this analysis, the analysis has not been done in a way that’s careful enough to have confidence in any of the results.”
Asked how Nature’s peer-review process had treated the species findings, a spokesman for the journal noted that the authors included a caveat that the list of species identified at the market was “not definitive” and more analysis was required.
For the international scientists who had first reported finding signs of raccoon dogs in the Covid-positive swabs last month, the latest Nature study left a number of important questions unanswered about the methods used by the Chinese team to analyze the sequences.
Still, the publication, as well as an earlier version of it posted online by the Chinese scientists last week, did supply critical new data, including the number of swabs taken from each stall in the market, said Alexander Crits-Christoph, a former postdoctoral researcher and computational biologist at Johns Hopkins University who helped lead the international team’s analysis.
With that information, Dr. Crits-Christoph said that he and his collaborators were able to confirm an important finding: Swabs taken from a corner of the market selling wild animals were more likely to test positive for the virus, a result that could not be explained merely by Chinese researchers having taken more samples from that corner, he said.
“It’s an extremely impressive data set and its importance is quite high,” Dr. Crits-Christoph said of the market samples. “And because of that, I think it’s a good thing this data has been published in the scientific record, even if I don’t agree with every interpretation.”
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