The very earliest cases of the COVID-19 pandemic have been pinpointed – vindicating one of the earliest theories about where the virus came from – by a team of 18 scientists, hailing from half a dozen countries.
In a new article, published in the journal Science, researchers identified the Huanan Seafood Wholesale Market in Wuhan, China, as the likeliest source of the outbreak. This aligns with some of the earliest reports of the pandemic, quickly dismissed by Chinese officials, which linked the then-novel coronavirus with the sale of live animals, such as bats, at the Market.
“These are the most compelling and most detailed studies of what happened in Wuhan in the earliest stages of what would become the COVID-19 pandemic,” Stephen Goldstein, a postdoctoral scientist in the department of Human Genetics at the University of Utah, and co-author of the study, said in a statement.
“We have convincingly shown that the wild animal sales at the Huanan Market in Wuhan are implicated in the first human cases of the disease.”
The team’s first piece of evidence for the finding comes from a study, originally published in early 2021 by the World Health Organization (WHO), on some of the very first reported cases of COVID-19. Of the 174 patients found by the WHO, the researchers were able to reverse-engineer the likely homes and workplaces of 155.
A clear pattern emerged. “The location of the Huanan market lies within the highest density contour that contains 1 percent of the probability mass,” explains the paper.
“The clustering of COVID-19 cases in December around the Huanan market… contrasts with the pattern of widely dispersed cases across Wuhan by early January through mid-February 2020,” the authors point out. “By January and February many of the sick who sought help resided in highly populated areas of the city, and particularly in areas with a high density of older people.”
All of that first group of patients lived closer to the Market than would be expected from a random sample of the population – and for cases without a known link to the Market, that effect was even stronger.
“The observation that a substantial proportion of early cases had no known epidemiological link had previously been used as an argument against a Huanan market epicenter of the pandemic,” note the authors. “However, this group of cases resided significantly closer to the market than those who worked there, indicating that they had been exposed to the virus at, or near, the Huanan market.”
But that’s not the only clue they found. Since the early days of COVID-19, there have been multiple lineages circulating – we’re currently all the way up to Omicron BA.5, but back in 2019 there were only A and B.
For a long time, the paper explains, only lineage B was known to have been present at the Market – but newer research has called that into question, with one preprint from this year confirming the presence of lineage A at the site.
If, as some have suggested, the Huanan market was simply an early super-spreader event for a virus that had originated elsewhere, it would be very surprising to see both lineages circulating like this. Instead, it’s much more likely that both lineages originated independently at the market, with the first cases potentially occurring as early as November 2019, the researchers say.
Add this to the results of spatial analyses within the market, and it all suggests that the source of the COVID-19 pandemic was most likely one or more of the small group of stalls in the southwest corner of Huanan Market – the section where traders sold live mammals, including raccoon dogs, hog badgers, and red foxes, and where multiple positive samples from the stalls and nearby drainage systems were taken.
“The pattern of COVID-19 cases reported for the Huanan market, with the earliest cases in the same part of the market as the wildlife sales and evidence of at least two introductions, resembles the multiple cross-species transmissions of SARS-CoV-2 subsequently observed during the pandemic from animals to humans on mink farms, and from infected hamsters to humans in the pet trade,” the researchers write.
“The live animal trade and live animal markets are a common theme in virus spillover events, with markets such as the Huanan market selling live mammals being in the highest risk category,” they continue. “To reduce the risk of future pandemics we must understand, and then limit, the routes and opportunities for virus spillover.”