The origins of Covid-19 are more complicated than we thought

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 in central China’s Hubei Province. The market would have presented a confusing environment to the uninitiated: rows of stalls selling unknown creatures for food, both dead and alive; Cages with pig badgers and Siberian weasels, Malayan porcupines and masked civet cats. In the south-west corner of the market, Holmes found a stall selling raccoon dogs caged on top of another, housing a species of bird he did not recognize. He paused to take a picture.

Eight years later, this photo is important evidence of the painstaking effort to trace the coronavirus pandemic back to its origins. Of course, Wuhan’s wet market has been suspected to have played a role since the early days of the pandemic – even before there was a pandemic – but it has been difficult to prove conclusively. Meanwhile, other origin theories have blossomed, centering on the Wuhan Institute of Virology, a biological research lab that accidentally or intentionally unleashed the virus on the city and the world.

The overwhelming scientific consensus is that Covid emerged in a similar fashion to related diseases like SARS, which jumped from bats to humans via an intermediate animal. Finding out exactly what happened to Covid-19 could prove immensely valuable, both in terms of definitively debunking the lab leak theory and as a source of information on how to stop the next pandemic. “It’s not about assigning blame,” says Kristian Andersen, professor of immunology and microbiology at the Scripps Research Institute in California. “The point here is to understand the origins of the Covid-19 pandemic in as much detail as possible.”

For the past two years, an international team of scientists, including Andersen and Holmes, have attempted to pinpoint the epicenter of the pandemic, using methods ranging from genetic analysis to social media scraping. Her research, which was widely shared in preprint before being published in its final form last week, reads like both a detective report and a scholarly study.

First: the crime scene. 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, combed through a report released by the World Health Organization in the summer of 2021, based on a joint investigation by the public health agency and Chinese scientists. By cross-referencing the various maps and tables in the report, the researchers obtained coordinates for 155 of the earliest Covid cases in Wuhan, people who were hospitalized for the disease in December 2019.

Most of these cases were clustered around central Wuhan, particularly on the west bank of the Yangtze River — the same area as Huanan Market. “There was this extraordinary pattern where the highest case density was both extremely close to the market and very centered on the market,” says Worobey, lead author of the paper, which was published in Science. Statistical analysis confirmed that it was “extremely unlikely” that the pattern of cases observed in the early days of the pandemic would have been so common in the market had Covid originated elsewhere: a random selection of similar people from the local area from Wuhan was very unlikely to have lived so close to the market.

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