It starts with a simple cough,

and before you know it,

millions of people are infected.

And it won't stop there.

It could keep growing

and growing

until billions of people are sick.

Flights are canceled,

cities are quarantined,

and hospitals are flooded with patients.

This is what's known as a global pandemic.

Could we experience something like this?

A worldwide pandemic like this

wouldn't be new to the human race.

It happened in 1918

and was known as the Spanish flu.

It infected about one-third

of the global population

and killed an estimated 50 million people.

So before we start completely freaking out

about the end of the world,

you can take a bit of comfort in knowing this

most likely doesn't mean the end of civilization.

But that doesn't mean there won't be consequences.

Before we get to what might happen,

how does a pandemic start anyway?

Widely spread epidemics in the past,

like the Spanish Flu

as well as SARS in 2003,

began with a strain of influenza,

or, "the flu."

There are two main types of influenza.

Type A

which typically comes from animals,

including birds, cats, pigs and horses.

And type B viruses

which are only common among humans.

The symptoms of a virus like this

are things we've all experienced

runny nose, fever, headache,

and just general cold symptoms.

But in other cases,

influenza can also result

in respiratory issues,

kidney failure

or even death.

But keep in mind those aren't guaranteed to happen.

A disease like this

could infect over 2.5 billion people.

Why so many?

The main thing about these influenza strains

is that they can be carried through the air.

If someone has it

and breathes in your direction,

you could breathe in microscopic

water droplets carrying the virus.

Or, if you touch a surface

that has the virus on it

and then touch your face,

you could also catch the disease.

You might not even feel the symptoms of influenza right away.

It could take a few hours

or even up to two weeks.

This means you'd be interacting with people as usual

and unknowingly be infecting them.

And today the world is a lot different

than it was during 1918's Spanish Flu.

In addition to the world's population being much higher,

we also live very differently.

Cities are much more dense,

with places like Mumbai

having over 76,000 people per square mile.

With people living closer together,

it means we can infect each other more easily.

Not only that,

but we travel the world with ease now.

People who unknowingly carry a virus

can quickly bring it to the other side of the world.

If this new virus were to spread

to just a single person,

who spread it to another single person

and another, and another.

As time went on,

it would eventually infect millions.

As people got infected,

planes would be grounded,

and entire countries could be quarantined.

If it got bad enough,

we might not even be able to leave our homes

due to the risk of infecting people

or getting infected ourselves.

Getting help at a hospital

could be difficult too.

With billions of people infected,

it's unlikely hospitals would be able to care for everyone.

If we're dealing with a pandemic that spreads the same way as the Spanish flu did,

we could anticipate

anywhere between 200 to 425 million deaths.

And that's out of the approximately

2.5 billion people who would be infected.

But how likely is it

that a scenario like this will happen?

Well, it's hard to say.

Experts say that humanity is due for a massive pandemic.

It happened 100 years ago with the Spanish flu,

and before that

with the bubonic plague in 1347.

Unfortunately,

pandemics like these are just a reality of human civilization.

But that doesn't mean a pandemic today would

be as bad as the Spanish flu.

Although the disease might

spread more efficiently than ever before,

it also might be easier than ever to cure it.

Although a pandemic implies that

you'll have little immunity to it,

doctors could develop a vaccine for it.

Today, with increased technology and

communication being more seamless than ever,

the world's scientists could work together.

You could have doctors in New York talking with

researchers in China trying to solve a pandemic.

It definitely wouldn't be easy and

could take up to a year,

but eventually,

a vaccine could be invented.

The next issue would be

how it gets distributed.

If countries aren't willing to work together

and distribute the vaccines fairly,

it could cause some serious conflict.

But assuming they all do work together,

it could eventually stop the pandemic.

Hopefully, something like this won't happen in the first place.

After all, we're now better at

monitoring animals and their diseases than ever before.

And by knowing the consequences of a real pandemic,

hopefully, we can stop the spread of infections before they go any further.

So how can you avoid something like this?

Well, according to health experts,

the rules are pretty simple.

Similar to avoiding the common cold,

you should wash your hands a lot

and keep away from people coughing and sneezing.

And if you're feeling sick,

you should definitely see a doctor right away

Also, would you please cough and sneeze into a tissue or elbow?

So although everybody doesn't have to die in this scenario,

it would have a severe impact on people.

And if the world isn't willing to work and cooperate together,

the realities of a new pandemic

could be pretty grim.

Want to know something that isn't so grim?

How about traveling to Mars?

We'll leave that story for another WHAT IF.