- [Narrator] A seafood market,

a virology lab, and a mine deep in the mountains.

Key events at these places in China could be crucial

to understanding how a small cluster of coronavirus cases

ended up sweeping the world.

Because almost a year and a half

into this global health crisis, politicians and scientists

are still debating how it all started.

- [Betsy] If you're gonna look for the origin of a pandemic,

you really should start right away when the clues are fresh.

Right now that's looking pretty difficult.

- [Narrator] That's because access to Wuhan

has been really limited.

- Until you nail it down definitively,

you've always got to keep an open mind

that it might be something else.

- [Narrator] The main hypothesis

is that the virus originated from bats.

Jumped to another animal, then to us.

And the leap to humans

might've happened here at this market.

10 miles away is where some scientists believe

that the virus may have accidentally leaked from a lab.

And both of these spots in Wuhan

have an increasingly important connection to one place

that's over 1000 miles away

in the mountains of Yunnan province.

So we visit these key places

to break down what we know about the coronavirus

to understand how the global pandemic may have started.

Stop number one, the Huanan Seafood Market,

December 31st, 2019.

This is the day the WHO learned

about a cluster of pneumonia cases in Wuhan.

And increasingly, the focus was on the market.

The complex spans an area that's the size

of nine football fields and has over 600 stalls.

About 10 of those were selling wild animals

like bamboo rats, hedgehogs and hog badgers.

- [Betsy] These wildlife are raised on farms,

sometimes in crowded conditions

where it's easy for animals to spread viruses back

and forth between each other

and the viruses start to mix and match and can change.

- [Narrator] Some wildlife

that are receptive to coronavirus infections

are consumed in China,

either for food or used in traditional medicine.

- [Betsy] These animals are shipped to urban markets

where they are sold sometimes live and butchered onsite.

And all this contact with live possibly infected animals

or the infected fresh meat

has become a major concern in recent years.

- [Narrator] And in Wuhan, many of the first cases

were either vendors who worked at the market,

or people who had shopped there.

By January 1st, Chinese authorities shut the place down.

- [Betsy] Well, originally Chinese authorities did feel

that it possibly came from the Huanan Market

and from wild meat of some sort.

- [Narrator] About three weeks later,

scientists in Wuhan and Beijing published

a pivotal paper in the medical journal, The Lancet.

This chart shows how some of the early cases

were people who hadn't been at the market.

More than a year later, there was new data

to piece together a clearer picture,

that's because China allowed

a group of international scientists to come to Wuhan

for several weeks to visit the market and hospitals.

- [Betsy] A team from the WHO that visited China

also learned going through the data

that by mid to late December,

the viruses that were infecting people

were genetically different enough

that they knew it wasn't all coming from the same place.

- [Narrator] The WHO said the presence

of early cases not linked to the market could suggest

that it was not the original source of the outbreak.

And increasingly, one place a team visited

is at the center of another hypothesis,

the Wuhan Institute of Virology.

- This is a world-class Institute

with high security laboratories

and does a lot of work with scientists outside of China,

very vibrant collaboration before the pandemic.

They would travel to caves where bats are known to roost

and take samples, and then study them in their lab.

- [Narrator] These bat coronaviruses and pathogens

are cataloged in databases.

The researchers used this library of information

to compare it to blood samples

and oral swabs from patients in Wuhan.

And about a month after the market was closed,

these researchers discovered that COVID-19

had a 96.2% genetic match with the bat coronavirus

that the institute had found back in 2013.

Scientists around the world consider this

a breakthrough in the search for COVID-19 source,

because it strongly indicated

that it could have originated in bats.

- This laboratory studies bat coronaviruses right in Wuhan,

was an obvious question, could it have escaped?

And even the Institute's own researchers asked that question

and went and did their own research.

- [Narrator] As questions swirled

around a possible accident at the institute,

it's top bat coronavirus expert said

the virus didn't leak from her labs,

and none of its staff have tested positive for COVID-19.

- These are not the first times

that we've had a world exposed to virus

as a result of failures in a Chinese lab.

- Last year, what started out as a basic scientific question

got politicized with a lot of finger pointing at China

yet there was no evidence presented.

(journalists chattering)

- [Man] Anything sir.

- [Narrator] And there was also limited access to data

during the WHO-led team's trip to Wuhan.

One of the stops was the virology institute.

- They asked questions and they had a tour,

but they didn't get any firsthand look

at databases, medical records, any sort of raw data

which would have shed light

on whether the virus could have escaped or not.

- [Narrator] Almost a week later,

scientists summed up their findings at a press conference.

They said the spillover from an intermediate host to humans

was likely to very likely,

and as for questions surrounding the lab.

- The findings suggest

that the laboratory incident hypothesis

is extremely unlikely.

- [Narrator] But later, the WHO chief said

the team didn't sufficiently examine the lab hypothesis,

and called for a fuller probe.

Three months later after that press conference,

a group of leading virologists and epidemiologists

wrote a letter saying there were no findings

in clear support of either

a natural spillover or a lab accident.

- This group of people is not saying

that they believe it came from a lab.

What they're saying

is that there's not enough evidence to rule it out.

Scientists investigate hypotheses

and they rule them out one by one.

And they just said that process hasn't been able to happen

and it needs to happen.

(speaking in foreign language)

- [Narrator] China says it's cooperated fully

with the effort to search for COVID-19's source

and has urged the WHO

to investigate early cases in other countries.

(bright music)

And one place that could provide some new evidence

for both hypotheses, Yunnan.

It's China's Southwestern most province

and home to many coronavirus-carrying bats.

And could set the stage for where the investigation

into the origin of the virus could go next.

- It's clearly an area where coronaviruses are circulating,

including coronaviruses that are very closely related

to SARS, the epidemic in 2003.

- [Narrator] Researchers

from the Wuhan Institute of Virology went to Yunnan

to study large bat populations inside caves.

In these crowded spaces, viral strains can mix together,

and become the building blocks of coronavirus

that then jump to humans.

- [Betsy] And at the same time,

there are wildlife farms there

that supply animals to Wuhan.

- [Narrator] Scientists say, this could explain how a virus

from a bat cave leapt to an intermediate host

then made its way to the market.

There was also a mine in Yunnan where scientists

from the institute spent some time from 2012 onwards.

It's where six miners who'd been clearing bat droppings

had gotten sick, and developed an unexplained pneumonia.

Three of them died.

So in 2013, scientists from the Institute went to the cave

to collect samples from bats.

A virus from one of these samples turned out

to be that 96.2% genetic match

that was discovered by the institute, inhaled as a big break

during the early days of the pandemic.

It took months for the institute

to reveal that the bat coronavirus samples

were from the mine, and that there were sick miners.

- The failure to describe it more

became kind of a touchpoint

for people who wanted more information

from the laboratory about the viruses they do have,

and what work they've been doing with them.

- [Narrator] Then, there was another allegation

about the institute that surfaced more than a year later.

- What US intelligence officials learned

is that there were three researchers

who became ill enough to seek hospital care.

They had symptoms that were like COVID,

but the symptoms like COVID are also like flu symptoms.

And flu was definitely circulating in Wuhan at that time.

- [Narrator] Four days after the intelligence report

about the sick lab workers, the Biden administration ordered

a US intelligence inquiry into the two scenarios.

China said the report was untrue.

(speaking in foreign language)

- Some people don't believe China

and say this has to be a coverup.

Others say we just need to verify,

though that's what we do in science.

We verify, we look at the data and reach our own conclusion.

It really does boil down to a question of transparency.

- [Narrator] So for any progress to be made

in the origins of the virus,

it'll ultimately require more data,

and fuller access to where it was first detected in China.

(bright music)