Camp Devens, Massachusetts.

The man on the autopsy table has turned blue.

Dr. William H. Welch nods to proceed.

His colleagues reach for the bone saw

and begin to open the ribcage.

The man's lungs are heavy.

Welch and his colleagues lean in as they're opened.

The lungs are so full of fluid

that it's traveled up the trachea.

The man had drowned

in his own body,

just like the others.

Welch needs air.

He opens the door and stumbles around men lying on the floor.

There are no longer enough beds in the hospital.

Six thousand men, crammed at a facility meant for 1,200,

and they're turning blue.

This is a horror story;

one of the most frightening in history.

In 1918 a new disease emerged.

We still don't know exactly how or where it first began infecting humans,

but within months

it would spread across the planet,

from the trenches of the Western Front to the most remote villages on earth.

It infected 1/3 of the world's population and killed between 50 and 100 million people.

To put that in perspective,

the low estimate would make it twice as deadly as World War I,

while the high estimate would mean it killed more than both World Wars combined.

Between 3-6% of the global population

died within 18 months.

It was the first modern plague,

turning our interconnected world against us

by spreading through shipping lanes,

rail lines

and the arteries of industrialized war,

yet it was also the first pandemic of the scientific age,

where doctors could,

to some extent,

understand what was happening

and stand against the infection,

though they lacked the tools to stop it.

So in 1918,

while researchers couldn't really see viruses,

they knew such things must exist.

They had no idea that unlike the bacteria they could see in their microscopes,

the flu was not alive in any way humans understood it:

Just a bunch of unstable genetic material that possessed a cell, forcing it to pump out

billions of copies of itself,

and with each cell infected,

a minority of those new viruses mutated into something more infectious;

more deadly.

A microorganism that,

through the randomness of natural selection,

became progressively better at catching and killing as it passed through each host.

In its wake it altered a World War,

drove languages extinct,

and shattered the sense of invulnerability that modern medicine had begun to cultivate,

and when the nightmare ended,

the world did what any person does when they wake from a dream:

It forgot!

But forgetting is something we can't afford

because the virus that ravaged the world in 1918 is still out there;

still mutating,

and it will return.

Yet, despite its impacts,

we still don't know where the pandemic originated,

but there are theories!

Canada, 1917.

A train races across the plains.

Military guards are instructed to keep civilians away from the locomotive.

If they see what's inside,

there may be a riot.

These cars, designed for cattle,

contain the men of the Chinese Labor Corps.

Pawns in a political gambit,

until recently,

the young, fragile Republic of China had remained neutral in the first World War.

With so many foreign countries holding territory within its borders,

joining the conflict

risks making their homeland

a battleground.

But neutrality was not tenable.

Japan, one of the allies,

had used the war as pretext to move troops

into Chinese territory

and demand control of the Chinese government.

To thread the political needle, China had declared war on Germany.

Hopefully the other allies will now protect China

from Japanese aggression and give it a seat at the post-war negotiating table.

It may even get its occupied territory back.

But to maintain a shred of neutrality,

these Chinese recruits are barred from combat.

They would dig trenches,

lug ammunition, and clear minefields.

So here they are,

shipped to Canada,

crammed on train cars,

and traveling overland to a troop ship in Halifax.

But there's something else among them.

A respiratory disease that had ravaged northern China the previous year.

A winter sickness

severe enough that some victims coughed blood and turned blue.

First, one recruit begins to cough,

then another.

One by one they fall ill with splitting headaches and chills.

Crammed into the cattle cars, there's nowhere to run;

nowhere to isolate the sick.

They beg the guards to let them get off and seek medical attention,

but due to the rampant anti-Chinese sentiment in Canada,

the guards have their orders to keep the passengers a secret.

By the time they reach Halifax,

3,000 have to be placed in quarantine.

Doctors give the sick nothing but castor oil for sore throats

and load the rest of the recruits onto the troop ships for France.

Those men aren't sick...

yet.

But flu victims are contagious days before presenting symptoms,

meaning the British Empire has just delivered Pandemic flu

to the trenches.

If that is,

it was flu,

because another emergence is about to occur in the unlikeliest of places.

March 4th, 1918.

Camp Funston, Kansas.

Like every military base in America,

Camp Funston is overcrowded.

The second largest training center in the country,

Funston's 56,000 men live in barracks and tents,

each waiting to be rotated to duty in the US or France.

Diseases always break out when recruits muster for war,

so it's no surprise when a private,

a Cook no less, reports for sick call with influenza.

By noon, 107 other soldiers have joined him.

Within three weeks it'll be over 1,100.

Alarming, sure, but this is wartime.

Camp outbreaks happen.

Even as 20% of the patients develop pneumonia and 38 died

Doctors see nothing abnormal,

but they're missing a key piece of the puzzle.

A month before and 300 miles away,

the lone doctor in Haskell County, Kansas had watched flu kill dozens of his strongest,

healthiest patients.

It's rapid pace and high fatality rate alarmed him so much,

that he contacted the Public Health Service

and published an alert in the National Health Journal,

but no one listened!

The paper's obituary page was unusually busy that February,

but alongside the reports of death and illness were heartwarming articles.

Soldiers from Haskell County were departing for boot camp

or visiting home one last time before deployment.

All headed to Camp Funston,

and from there, to France.

Two weeks after the first case at Funston,

10% of recruits were reporting sick at two camps in Georgia.

By the end of the month,

24 of the 36 largest military bases in America had cases,

along with 30 major cities.

No one noticed...

yet.

Army Medical Department,

Washington, DC.

Doctor William H. Welch was tracking an epidemic.

One of the country's most famous doctors, Welch had helped drag American medicine into the modern age.

He helped found the Johns Hopkins School of Medicine,

spread the use of microscopes,

and organized the Rockefeller Institute,

the country's first dedicated medical laboratory.

His work had helped transform America from a nation of country doctors

to a Titan of scientific medicine,

able to compete with the Pasteur Institute in France

and the Koch Institute in Berlin.

Because of him, America had joined the age of the microscope and the vaccine,

a bright world where doctors could both see diseases and kill them.

The last few decades had brought vaccines for smallpox, rabies, anthrax, diphtheria, and meningitis.

Researchers at the Rockefeller Institute were taking the first steps towards limb reattachment

and organ transplantation.

Some optimists even predicted a future without communicable disease!

And America needed that scientific power now more than ever!

Even before the war,

Welch delivered a message to the Army Surgeon General:

When mobilization happens,

you'll have an epidemic!

You'll need to recruit the best doctors and microbiologists.

You'll need researchers,

train cars outfitted as mobile research laboratories,

a stockpile of vaccines and antitoxins,

anything to be ready.

When the war started,

the Surgeon General didn't bother recruiting Welch and his researchers.

He just unfolded the Rockefeller Institute into the army.

And here it was, the epidemic that Welch had feared.

He could see it moving on the map from camp to camp,

and it had killed nearly 6,000 already.

He had sent researchers to chart the spread

and battle the secondary cases of pneumonia that were the real killer in most epidemics.

They'd all warned the army that this would happen if they overcrowded the camps,

but no one listened!

Welch had dispatched an experimental vaccine that fought one form of bacterial pneumonia,

as well as a serum that cut the death rates by half.

Results of the test looked good, if not 100% effective.

It was proving a successful response.

But there was a problem.

Because the epidemic that Welch was fighting to contain wasn't flu,

it was measles.

He'd seen reports of influenza spreading too, but

influenza was seasonal,

something that was expected and would go away.

Doctors weren't even obligated to report cases to the Public Health Service,

so the prospect of a measles outbreak seemed much more serious,

especially with recruits grouped together in training camps

and 36,000 of the nation's doctors deployed in France.

So as Welch fought Measles,

infected American troops boarded troop ships.

They packed into the hold until each converted ocean liner held twice the normal load of passengers.

They pulled away from the dock

waving farewell to families and loved ones on shore

and turned towards Europe.

It was in the bloodstream now.

Not just of the men,

but of the world...