In October 2014, virologist Edward Holmes took a tour of the Huanan Seafood Wholesale Market in Wuhan, a once relatively overlooked city of about 11 million people in the central Chinese province of Hubei. The market would have presented a bewildering environment for the uninitiated: rows of stalls selling unfamiliar creatures for food, both dead and alive; cages holding hog badgers and Siberian weasels, Malayan porcupines and masked palm civets. In the southwest corner of the market, Holmes found a stall selling raccoon dogs, stacked in a cage on top of another housing a species of bird he didn’t recognize. He paused to take a photo.
Eight years on, that photo is a key piece of evidence in the painstaking effort to trace the coronavirus pandemic back to its origins. Of course, it’s been suspected since the early days of the pandemic—since before it was even a pandemic—that the Wuhan wet market played a role, but it’s been difficult to prove it definitively. In the meantime, other origin theories have flowered centered on the Wuhan Institute of Virology, a biological research lab which, it’s argued, accidentally or deliberately unleashed the virus on the city and the world.
The overwhelming scientific consensus is that Covid originated in a similar way to related diseases such as SARS, which jumped from bats to humans via an intermediate animal. Figuring out exactly what happened with Covid-19 could prove immensely valuable both in terms of finally disproving the lab leak theory and by providing a source of information on how to stop the next pandemic. “This is not about placing blame,” says Kristian Andersen, a professor of immunology and microbiology at the Scripps Research Institute in California. “This is about understanding in as much detail as we can the origins of the Covid-19 pandemic.”
For the last two years, an international team of scientists including Andersen and Holmes has been trying to pinpoint the epicenter of the pandemic, using methods ranging from genetic analysis to social media scraping. Their research, which attracted widespread coverage in preprint before being published in its final form last week, reads as much like a detective report as an academic study.
First: the scene of the crime. Where exactly in this city of 11 million people did the virus first jump from animals to humans? To find out, the team—led by University of Arizona biologist Michael Worobey—scoured a report published by the World Health Organization in the summer of 2021, which was based on a joint investigation the public health body conducted with Chinese scientists. By cross-referencing the different maps and tables within the report, the researchers obtained coordinates for 155 of the earliest Covid cases in Wuhan, people who were hospitalized from the disease in December 2019.
Most of those cases were clustered around central Wuhan, particularly on the west bank of the Yangtze river—the same area as the Huanan market. “There was this extraordinary pattern where the highest density of cases was both extremely near to and very centered on the market,” says Worobey, lead author on the paper, which was published in Science. Statistical analysis confirmed that it was “extremely unlikely” that the pattern of cases seen in the early days of the pandemic would have been so clustered on the market if Covid had originated anywhere else: A random selection of similar people from around Wuhan were very unlikely to have lived so close to the market.