Raccoon dogs—known to be susceptible to COVID-19, and to spread viruses to humans—are thought to have been sold illegally at the market. They could be the missing link in the chain of transmission from bats, presumably, to people, experts in the zoonotic transmission camp say.

But WHO officials Friday cautioned against assumptions, saying that while the information is an important piece of the proverbial jigsaw puzzle, “it does not determine what the picture shows”—and that a lab leak can’t be ruled out.

“The more pieces you have in the right place, the more you start to see an image,” Dr. Michael Ryan, the organization’s executive director of health emergencies, said at a news conference, referencing the puzzle analogy. 

“You’re never really sure what you’re building until you put a piece in the context of all the other pieces,” he said. But “your level of confidence grows as you put it together.”

No definitive answer

The WHO on Sunday was made aware of data from samples taken at the Huanan Seafood Market in Wuhan during the early days of the pandemic, before the market was shut down. That data been published to GISAID—an international research database that tracks changes in COVID and the flu virus—by officials with the Chinese Center for Disease Control and Prevention in late January, but was recently taken down, Dr. Tedros Adhanom Ghebreyesu, WHO director general, said at the news conference.

The knowledge triggered a Tuesday meeting of WHO’s Scientific Advisory Group for the Origins of Novel Pathogens, which is investigating the virus’s origins. At the meeting, international scientists who had obtained the data before it was removed and analyzed it presented their findings. Chinese CDC officials also presented, at the WHO’s request.

The new information provides no definitive answers as to the pandemic’s origins, Ghebreyesu cautioned. “But every piece of data is important in moving us closer to that answer.”

All data related to studying the novel virus’s origins “needs to be shared with the international community,” he said. “The data could have—and should have—been shared three years ago.”

The data shows only that raccoon dogs were present at the market, in addition to other animals and the virus, Maria Van Verkohove, technical lead for COVID-19 at the WHO, said.

While it’s the first bit of molecular evidence that animals were illegally sold at the wet market, it’s not proof that such animals—or any animals—were infected, she said. Had they been, it wouldn’t necessarily mean they brought the virus to the market. They may have been infected by humans, at the market or elsewhere.

“It just tells us that more data exists, and that data needs to be shared in full,” she said.

A February 2022 preprint article, not peer reviewed, published by the Chinese Academy of Science’s George Gao, the former head of the country’s CDC, and a litany of other researchers from the country details 1,380 samples collected from the environment and animals at the Huanan Seafood Market in Wuhan in early 2020. 

A total of 73 environmental samples were positive for COVID-19. The virus was not detected in the 18 animal swabs collected there, according to the report.

A ‘smoking gun’

Dr. Georges Benjamin, executive director of the American Public Health Association, told Fortune that the new information is “strong evidence” supporting the theory of transmission of the virus from animals to people.

Proof that “raccoon dogs, a known transmitter of viruses to humans, were in an illegal wet market is a smoking gun,” Benjamin said.

Dr. Raj Rajnarayanan, assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., called the report “a key piece of the puzzle,” adding that it will allow virus trackers the ability to “establish a timeline” of evolution.

While the new information doesn’t solve the puzzle, it provides significant hope that the puzzle can, indeed, be solved, Benjamin said. “It will take some painstaking research and science to do it. But now we have a pathway to figure it out.”

Not everyone, however, agrees on the information’s utility—at least not yet. Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security, told Fortune that the scientific community at large still doesn’t have access to the data recently pulled from the international research database by Chinese officials. 

Thus, there isn’t “enough information to be able to really say anything useful” about the report of raccoon dog DNA at the market, Adalja said. “No evidence has actually been presented as of yet.”

If the data is, indeed, scientifically valid, “it would lend support to the consensus view that COVID-19 likely spilled over from an animal into a human without there being any lab accidents or intentional release,” Dr. Jay Varma, chief medical adviser at the New York-based think tank Kroll Institute, told Fortune.

But it’s possible that raccoon dogs are nothing but a red herring, when it comes to determining the origins of COVID, Varma cautions. 

There have been anecdotal reports of “COVID or COVID-like illness” not tied to the market occurring as far back as November 2019—before the market’s super-spreading events in December.

Those cases could signal that COVID-19 didn’t spill into humans from the market—or that such spill-over wasn’t responsible for the first human cases of COVID.

Varma spent three years in China with the U.S. Centers for Disease Control and Prevention, working on the issue of respiratory virus circulation in central China. He says he’s always thought there were multiple spill-overs from animals to humans in the region between October and December 2019.

An outbreak occurred at the market, he said. But it may not have started there.

Spillovers may have occurred “someone else in and around Wuhan,” he said.