GEOFF BENNETT: Newly discovered genetic sampling from Wuhan, China, provides stronger evidence that COVID-19 moved from animals into humans back in 2019.

But the origins of the virus remain uncertain.

John Yang has the latest.

JOHN YANG: Almost from the beginning of the pandemic, the debate over its origin focused on two theories, that there was a natural source, that humans were first infected by a wild animal, or that the virus leaked from a lab.

Scientists say the natural transmission theory has been strengthened by new genetic evidence from the market in Wuhan, China, where there was a big COVID outbreak in December 2019.

Samples known to have the virus have also been found to have genetic material from animals, much of it from the common raccoon dog, a small animal related to foxes.

Katherine Wu first reported this in "The Atlantic", where she's a staff writer.

She also has a Ph.D. in microbiology.

Katherine, what is it that these scientists found that points them in the direction of a wild animal being the source?

KATHERINE WU, "The Atlantic": Right.

So this is another clue really strengthening the case for a natural origin for this virus, which is the case for so many other viruses.

Being able to take a swab at that market and extracting genetic material from both the virus and an animal known to be susceptible to the virus, as is the case for the raccoon dog, is a pretty good indication that an infection of that animal, potentially of these raccoon dogs, may have happened at the market at the time the pandemic began.

That's not exactly a smoking gun.

The strongest evidence for a true natural origin would really be being able to find evidence of a live infected animal, so, for instance, having a swab that has virus in it that was taken from an animal's mouth or nose, for instance, or maybe being able to find, for instance, an infected raccoon dog in the wild now.

That's not quite the case here, but it's pretty darn close.

Knowing that there were already viral samples at the market and knowing that raccoon dogs can catch and pass on this virus, this sort of helps bring that story together.

Now we know the virus and the raccoon dog were in so close proximity that we could get these swabs with genetic material from both.

That's pretty much like finding the fingerprints of a crime suspect at the scene of the crime.

JOHN YANG: Why is this coming out now.

The virus -- this is three years after the pandemic started.

KATHERINE WU: It's an incredibly important question, and I do not have a perfect answer for you.

The reason that we are getting this analysis now is that the researchers who did the new analysis were sort of piggybacking off of samples that were collected by Chinese researchers very early on in the pandemic, in January and maybe a little bit later of 2020.

Those researchers did originally analyze those samples, and they posted a preprint, a version of a study that hadn't yet been published with peer review in a scientific journal, in February of last year.

But that analysis didn't actually point to wild animals as a possible host for the virus.

And the raw data for that analysis wasn't made available at the time.

Now, more than a year later, researchers have been able to get their hands on that raw data, which seems to have been uploaded to a server quite recently, and reanalyzed it and been able to take animal -- been able to extract genetic sequences that point to the presence of a wild animal in those same samples.

So this is old sampling, but a new interpretation, a new analysis that is providing us with brand-new clues.

JOHN YANG: In recent weeks, we have had the U.S. intelligence community, the Energy Department come out and say that they thought it was coming from a lab, even though they -- we don't know how they reached that conclusion.

And they acknowledge that it was with a low degree of certainty.

Is this evidence going to be enough to convince the people who think it came from a lab, do you think?

KATHERINE WU: I honestly suspect probably not.

I hope that some people will be swayed.

But I think we do have to strike the balance here.

This is great evidence.

This is a new clue bolstering the natural origin hypothesis.

But, again, it's not the slam-dunk evidence that I suspect a lot of people have been looking for to really push them in one direction or the other.

Already, there's a reaction, especially online on social media from people who are more in favor of the lab leak idea, saying that this is not the end of the story.

The researchers also have yet to publish a full analysis and release the data.

And I think a lot of people in the research community are going to want to get their hands on that raw data.

There's a big question about why it took so long for that raw data to be uploaded.

And, also, now it has subsequently been removed from that same server, and it's not yet clear when it's going to reappear.

The World Health Organization has called for all data of this nature to be made available.

But it's a little bit unclear if there's going to be more of a trickle like this that could really clinch the case or not.

JOHN YANG: Why is it so important that we figure out where this virus came from?

KATHERINE WU: It's a great question.

And I think there's multiple reasons.

For one, it would really, really help us better understand the nature of the virus that we are still grappling with, that is still causing immense suffering around the world.

It would also ideally help us prevent future outbreaks that are this devastating.

We know that most outbreaks of infectious disease in our recent and very far past have been caused by wild animals passing the virus to us.

And that is not the fault of wild animals, necessarily.

We are constantly encroaching on their spaces.

We are eating them, trading them, breeding them, selling them, using their fur, using other materials from them.

And those relationships aren't always managed well.

And if it does turn out to be not a natural origin, and it does turn out to be somewhat related to a lab, that warrants action too.

Basically, this is a call upon us to change our practices to make sure that outbreaks of this nature don't happen in the future.

How are we going to stop that if we don't know exactly how the worst one started?

JOHN YANG: Katherine Wu of "The Atlantic," thank you very much.

KATHERINE WU: Thank you so much for having me.