Answering the question of whether the disease arose naturally from animals to humans, or was the result of a laboratory accident, is considered vital to preventing the next pandemic and saving millions of lives.
The first article analyzed the geographical pattern of covid cases in the first month of the outbreak, in December 2019, and showed that the first infections clustered around the Huanan market.
The second studied the genomic information of the first cases to analyze the early evolution of the virus, concluding that it was unlikely to circulate widely among humans before November 2019.
Both were previously published as preprints or “preprints”, but have now undergone scientific peer review and appear in a prestigious journal.
Michael Worobey of the University of Arizona and a co-author on both papers previously called in a letter for the scientific community to be more open to the idea that the virus was the result of a lab leak.
But the findings brought him “to the point where I now also think it’s just not possible that this virus was introduced in any other way than through the wildlife trade in the Wuhan market,” he told reporters on a call.
Although the previous investigation had focused on the live animal market, investigators wanted more evidence to determine that it was actually the source of the outbreak, not its amplifier.
This required a neighborhood-scale study within Wuhan to make sure the virus was “zoonotic,” meaning it jumped from animals to people.
The first study team used mapping tools to determine the location of most of the first 174 cases identified by the World Health Organization, finding that 155 of them were in Wuhan.
These cases were piling up around the market, and some of the first patients with no recent history of visiting the market lived very close by.
Mammals now known to be infectious, including red foxes, badgers and raccoon dogs, were all sold live on the market, according to the team.
– Two lineages –
They also linked positive patient samples from early 2020 to those on the west side of the market, which was selling live or freshly butchered animals in late 2019.
The early cases contrasted with how it spread to the rest of the city between January and February, which researchers confirmed by drilling into the Weibo app’s social media log data.
“This tells us that the virus was not circulating cryptically,” Worobey said in a statement. “It really originated in that market and spread from there.”
The second study focused on resolving an apparent discrepancy in the early evolution of the virus.
The researchers conclude that prior to February 2020, two lineages of the virus existed, A and B, and that both were the result of two separate transmission events to humans, both in the Wuhan market.
Previous studies had suggested that lineage B had evolved from lineage A.
Under this scenario, there were probably other animal-to-human transmissions on the market that did not manifest as covid cases.
The study concludes that it was unlikely that there was circulation in humans before November 2019.
Under this scenario, there were probably other animal-to-human transmissions on the market that did not manifest as covid cases.
“Have we disproved the lab leak theory? No, we haven’t. Will we ever know? No,” said co-author Kristian Anderson of the Scripps Research Institute.
“But I think the really important thing 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.”
