The research, published online Tuesday by the journal Science, suggests the Huanan seafood wholesale market was likely an early epicenter of the plague that has killed nearly 6.4 million people worldwide. Scientists conclude that the virus that causes COVID-19, SARS-CoV-2, probably spread from animals to humans two different times.

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“All of this evidence tells us the same thing: it points to this particular market in the middle of Wuhan,” said Christian Andersen, a professor in the Department of Immunology and Microbiology at Scripps Research and co-author of one of the studies. “I was pretty convinced about the lab leak, until we looked at it very carefully and looked at it much more closely.” Story continues below ad In one study, which incorporated data collected by Chinese scientists, University of Arizona evolutionary biologist Michael Worobey and his colleagues used mapping tools to estimate the locations of more than 150 of the first reported cases of COVID-19 since December of 2019. They also mapped cases from January and February 2020 using data from a social media app that had created a channel for people with COVID-19 to get help. They asked, “Of all the locations where the first cases could have lived, where did they live? And it turned out that when we were able to look at that, there was this extraordinary pattern where the highest density of cases was both close and very concentrated in that market,” Worobey said at a news conference. “Mainly, does this apply to all cases in December as well as cases with no known market connection? And this is an indication that the virus started to spread among people working in the market, but then it started to spread in the local community.” Trending Stories

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Andersen said they found clusters of cases within the market as well, “and that the clustering is very, very specific to the parts of the market” where they now know people were selling wild animals, such as raccoon dogs, that are susceptible to infection with the coronavirus. 5:07 Health Matters: New studies on COVID-19 vaccines and children Health Matters: New studies on COVID-19 vaccines and children In the other study, the scientists analyzed the genomic diversity of the virus inside and outside China starting with the first genome samples in December 2019 and extending to mid-February 2020. They found that two lineages — A and B — marked the beginning of the pandemic in Wuhan. Study co-author Joel Wertheim, an expert in virus evolution at the University of California, San Diego, pointed out that the A lineage is most similar genetically to bat coronaviruses, but the B lineage appears to have started spreading earlier in people, especially in the market. Story continues below ad “Now I realize it sounds like I just said that a once-in-a-generation event happened twice in short succession,” Wertheim said. But there were certain conditions – such as humans and animals in close proximity and a virus that can be transmitted from animals to humans and from person to person. Thus, “barriers to diffusion have been reduced so that we believe many imports should be expected,” he said. Many scientists believe that the virus jumped from bats to humans, either directly or through another animal. But in June, the World Health Organization recommended a deeper investigation into whether a lab accident might be to blame. Critics had said the WHO was too quick to dismiss the lab leak theory. “Have we disproved the lab leak theory? No, we haven’t,” Andersen said. “But I think what’s really important here is that there are possible scenarios and there are plausible scenarios and it’s really important to understand that possible doesn’t mean equally likely.” The origin of the pandemic remains controversial. Some scientists believe a lab leak is more likely, and others remain open to both possibilities. But Matthew Aliotta, a researcher at the University of Minnesota’s college of veterinary medicine, said in his mind the pair of studies “kind of puts to work, hopefully, the lab leak hypothesis.” “Both of these studies provide really strong evidence for the natural origin hypothesis,” said Aliota, who was not involved in either study. Since sampling an animal that was on the market is impossible, “this is probably as close as you could get to a smoking gun.” © 2022 The Canadian Press