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Two of the reports trace the outbreak back to a massive market that sold live animals, among other goods, in Wuhan, China1,2, and a third suggests that the coronavirus SARS-CoV-2 spilled over from animals — possibly those sold at the market — into humans at least twice in November or December 20193.
Taken together, these different lines of evidence point towards the market as the source of the outbreak — much like animal markets were ground zero for the severe acute respiratory syndrome epidemic of 2002–2004 — says Kristian Andersen, a virologist at the Scripps Research Institute in La Jolla, California, and an author on two of the reports.
One of the studies he coauthored2 suggests that raccoon dogs were sold in a section of the market where several positive samples were collected.
Some virologists say that the new evidence pointing to the Huanan market doesn’t rule out an alternative hypothesis.
He says searching for SARS-CoV-2 and antibodies against it in blood samples collected from animals sold at the market, and from people who sold animals at the market, could provide more definitive evidence of COVID-19’s origins.
In early January 2020, Chinese authorities identified the Huanan market as a potential source of a viral outbreak because the majority of people infected with COVID-19 at that time had been there in the days before they began to show symptoms, or were in contact with people who had.
A research team from China including the head of China’s Center for Disease Control and Prevention has now genetically sequenced those positive samples, releasing the results in a preprint posted on 25 February1.
They arrived at this conclusion by compiling information on the first known COVID-19 cases in China, as reported in various places, including the WHO investigation, newspaper articles, and from audio and video recordings of doctors and patients in Wuhan.
They also examined the locations of the positive samples collected in the market, as reported in the WHO study, and fleshed out information about their potential surroundings by collecting business registration information, photographs of the market before it closed, and scientific reports that have emerged since the WHO’s investigation.
One of the coauthors on the report, virologist Eddie Holmes at the University of Sydney in Australia, had been to this stall in 2014 and snapped photographs — included in this study — of a live raccoon dog in a metal cage, stacked above crates of poultry, with the whole assembly sitting atop sewer drains.
In a second report3, Andersen and colleagues concluded that lineage A and lineage B of SARS-CoV-2 are too different from one another on a genetic level for one to have evolved into the other quickly in humans.
Taking all of the new data together, and adding a degree of speculation, Andersen suggests that raccoon dogs could have been infected on a farm that then sold the animals at the markets in Wuhan in November or December 2019, and that the virus might have jumped to people handling them, or to buyers.
Back in May 2021, he led a letter published in Science6 in which he and other researchers pressed the scientific community to keep an open mind about whether the pandemic stemmed from a laboratory, a controversial hypothesis suggesting that SARS-CoV-2 was either created in a lab, or was accidentally or intentionally released by researchers at the Wuhan Institute of Virology.
Separate lines of analysis point to it, he says, and it’s extremely improbable that two distinct lineages of SARS-CoV-2 could have been derived from a laboratory and then coincidentally ended up at the market.
David Relman, a microbiologist at Stanford University in California, agrees that the preprints are not definitive, and that they exclude the possibility that people were infected prior to the outbreak at the market, but went undiagnosed.
Last July, for example, Chinese officials said that they planned to analyse patient blood samples from 2019, stored at the Wuhan Blood Centre — but if that study has been conducted, it has yet to be made public.