Two preprint studies released on Feb. 26 offer additional evidence that the coronavirus pandemic started at a market in Wuhan, China.
By analyzing data from several sources, scientists concluded that the virus came from animals and spread to humans in late 2019 at the Huanan Seafood Market. They added that no evidence supported a theory that the virus came from a laboratory in Wuhan.
“When you look at all the evidence together, it’s an extraordinarily clear picture that the pandemic started at the Huanan market,” Michael Worobey, D.Phil., a co-author on both studies and an evolutionary biologist at the University of Arizona, told the New York Times.
The two reports haven’t yet been peer-reviewed or published in a scientific journal. They were posted on Zenodo, an open-access research repository operated by CERN.
In one study, researchers used spatial analysis to show that the earliest COVID-19 cases, which were diagnosed in December 2019, were linked to the market. Researchers also found that environmental samples that tested positive for the SARS-CoV-2 virus were associated with animal vendors.
In another study, researchers found that two major viral lineages of the coronavirus resulted from at least two events when the virus spread from animals into humans. The first transmission most likely happened in late November or early December 2019, they wrote, and the other likely happened a few weeks later.
Several of the researchers behind the new studies also published a review last summer that said the pandemic originated in an animal, likely at a wildlife market. At that time, they said the first known case was a vendor at the Huanan market.
The new findings provide the strongest evidence yet that the pandemic had animal-related origins, Dr. Worobey told CNN. He called the results a “game, set and match” for the theory that the pandemic began in a lab.
“It’s no longer something that makes sense to imagine that this started any other way,” he said.
In a separate line of research, scientists at the Chinese CDC conducted a new analysis of samples collected at the market in January. They found that the samples included the two main lineages of the coronavirus. They posted the results in a report on the Research Square preprint server Feb. 26.
“The beauty of it is how simply it all adds up now,” Jeremy Kamil, a virologist at Louisiana State University Health Sciences, who wasn’t involved with the new studies, told the New York Times.
The initial spread of the coronavirus was like a firework, Dr. Worobey told CNN, starting at the market and exploding outward. The “overwhelming majority” of cases were specifically linked to the western section of the market, where most of the live-mammal vendors were located, the study authors wrote. Then COVID-19 cases spread into the community from there, and the pattern of transmission changed by January or February 2020.
When researchers tested surfaces at the market for coronavirus genetic material, one stall had the most positives, including a cage where raccoon dogs had been kept.
The study authors said the findings highlight the urgent need to pay attention to situations where wild animals and humans interact closely on a daily basis.
“We need to do a better job of farming and regulating these wild animals,” Robert Garry, one of the co-authors and a professor of microbiology and immunology at the Tulane University School of Medicine, told CNN.
That could include better infrastructure in places like markets where viruses spill over from animals to humans, he said. Surveillance is also key in preventing future pandemics by detecting new respiratory diseases in humans, isolating patients, and sequencing new virus strains.
“This is not the last time this happens,” he said.
A version of this article first appeared on WebMD.com.