The research teams also analysed the genetic code of the viral samples found in the market, and compared them to samples from patients in the early days of the pandemic. Looking at the variety of different mutations in the viral samples also provides clues.
The samples suggest, but do not prove, that Covid started more than once in the market with potentially two spillover events from animals to humans. The researchers say this supports the idea of the market as the origin, rather than the pandemic starting elsewhere with the market adding fuel to the fire in a superspreading event.
The scientists also used the mutations to build the virus’s family tree and peer into its past.
“If we estimate when do we believe most likely the pandemic started versus when do we believe most likely the outbreak at the market started, these two overlap, they’re one and the same,” says Prof Andersen.
In their scientific publication, the full genetic diversity of coronavirus seen in the early days of the pandemic was found at the market.
Prof Michael Worobey, of the University of Arizona, said: “Rather than being one small branch on this big bushy evolutionary tree, the market sequences are across all the branches of the tree, in a way that is consistent with the genetic diversity actually beginning at the market.”
He said this study, combined with other data – such as early cases and hospitalisations being linked to the market – all pointed to an animal origin of Covid.
Prof Worobey said: “It’s far beyond reasonable doubt that that this is how it happened”, and that other explanations for the data required “really quite fanciful absurd scenarios”.
“I think there’s been a lack of appreciation even up until now about how strong the evidence is.”