(NewsNation) — Dr. Anthony Fauci is maintaining he has an open mind about the origins of COVID-19, but pointed to “accumulating evidence” that it was transmitted naturally as opposed to through an accidental lab leak.

The U.S. intelligence community remains divided on a definite origin, partly because China has not been forthcoming with information about the outbreak and a wet market in Wuhan where it might have first spread.

“We may not ever get (definitive proof), and that’s one of the frustrating things,” Fauci said Thursday on “Elizabeth Vargas Reports.”

Fauci’s comments came on the heels of a new study published Wednesday that shows large amounts of the virus were mixed in with genetic material from racoon dogs at an outdoor wet market in Wuhan.

The research focused on swabs taken in Wuhan in the early days of the pandemic. Chinese researchers confirmed DNA from raccoon dogs and other animals was found in COVID-19 samples, especially from one corner of the wet market where exotic wildlife was sold.

The first version of the study was published in 2022 and did not mention finding any genetic material from racoon dogs in the swabs, The New York Times reported.

“The environmental swabs that were taken from that part of the market, where there’s photographic evidence that there were raccoon dogs there at that segment of the market, again is accumulating evidence that it was a natural occurrence,” Fauci said, “but you have to keep an open mind until you definitively prove one versus the other.”

The study adds to the raging debate of whether the virus came from a lab leak or natural transmission. However, it does not prove that the virus originated there.

No specific animal has yet been found to be the original source, which Fauci said it not unprecedented.

“It took years and years to find the original source of HIV in chimpanzees. It took several years in SARS-Cov-1, which came about in 2002, in 2003, to show that correlation between a bat to a civet cat to a human,” he said. “We still don’t know the primary origin of Ebola. We know what comes from an animal in the wild, but we don’t know what that is.”

Three years after the pandemic began, government officials have not arrived at a consensus on the origin of COVID-19.

A lab leak is now the lead theory at the FBI, with Director Christopher Wray saying recently, “The FBI has assessed, for quite some time now, that the origins of the pandemic are most likely a potential lab incident in Wuhan.”

The Department of Energy has made a similar assessment, albeit with low confidence.

But the U.S. government does not yet have one official finding, and a 2021 report from the Office of the Director of National Intelligence gives weight to both the natural transmission and lab leak theories.

Unless China is more forthcoming, Fauci says it will be difficult to find a definitive answer.

“It is entirely conceivable that they knew those animals should not have been in the market and they cleaned out the market,” Fauci said. “It really is unfortunate that the Chinese did not make this information widely available at least a couple of years ago.”

NewsNation correspondent Blake Burman contributed to this report.