The swabs were taken by scientists affiliated with China's Centers for Disease Control and Prevention in early 2020, shortly after Chinese authorities closed the live animal and seafood market. The raw data from the swabs remained secret until Chinese researchers quietly uploaded them to the international genetic data-sharing platform GISAID.
The data was first noticed by an international team of researchers on March 4 this year. But it wasn't until March 9 that they realized the data corresponded to samples taken at the Huanan Market around the start of the pandemic. The researchers belong to universities across the world, including the Scripps Research Institute, the University of Arizona and the Sorbonne.
Most of the positive samples were clustered in an area of the market that was previously identified as a hot spot for infections, and where live animals were believed to have been sold.
A number of species were identified in the analysis: red foxes, rabbits, cats, dogs, Amur hedgehogs, Malayan porcupines, Himalayan marmots, masked palm civets -- and raccoon dogs which are of particular interest to the researchers. Previous studies have shown not only that they can be infected, but that they shed a lot of virus once they are sick, infecting other animals.
But despite this rare access to samples collected early in the pandemic, the researchers have urged caution, and stressed the limitations of their study, which still awaits peer review.
The study cannot definitively prove that any of these animals were infected with SARS-CoV-2, the virus that causes Covid-19, or that any of these animals infected humans. In fact, some positive specimens from other parts of the market contained human DNA, suggesting that humans were also shedding the virus there.
The researchers said their conclusions are limited because they were only able to work with a partial dataset.
In many ways, their caution mirrors that of US intelligence agencies, which said in the Department of Energy report they could only assess that the virus may have escaped from a lab leak with "low confidence."
While the two theories continue to compete and the debate gets politicized, it is important to remember what is at stake: Understanding how the pandemic started can help us better prepare for and potentially prevent the next one.
One certainty is that the lack of transparency -- whether over the practices of laboratories or food markets -- is potentially dangerous for everyone.
Addressing the new research, WHO Director-General Tedros Adhanom Ghebreyesus said: "This data could have, and should have, been shared years ago. We continue to call on China to be transparent in sharing data and to conduct the necessary investigations and share results."
Speaking at a news briefing Friday, Tedros also said that the data is not conclusive.
"These data do not provide a definitive answer to the question of how the pandemic began, but every piece of data is important in moving us closer to that answer."
