Two new studies published Saturday offer more evidence that the coronavirus originated in a seafood market in Wuhan, China, in 2019.
The evidence suggests the virus originated in animals and spread to humans.
One study looked at the earliest known COVID-19 cases, which were diagnosed in December of 2019.
The second study suggests the first transmission could have happened as early as November of 2019, or early December.
Samples that tested positive for SARS-CoV-2 were strongly associated with live animal vendors.
A cage where raccoon dogs were kept was among one of the places in the market that had the most positive samples of the virus.
The study suggests that the virus likely started with two animal transmissions or more, before it was passed on to humans.
They likely involved a raccoon dog and another mammal.
There is some pushback against the studies.
Jesse Bloom, a virologist at the Fred Hutchinson Cancer Research Center, told the New York Times that the studies did not provide evidence that the animals at the Wuhan market had been infected with the virus.
A separate study published in November of 2021 found that the first known COVID-19 case was a vendor at the market.