on average, they would spread it to two or three other people.

Those two or three other people would, on average, spread it to another two or three.

And so on, and so on.

One out of every 200 people who became infected died.

In one year, this virus killed over two million people worldwide.

Now let's back up:

Imagine if the virus were even more contagious –

if every infected person passed it on to an average of four, or six people;

and if its fatality rate was much, much higher:

closer to three in ten.

This devastating scenario is smallpox.

Smallpox claimed hundreds of millions of lives in the 20th century alone,

and plagued humanity for centuries before that.

And then it was gone.

We completely wiped it out of existence.

So, how did we do it?

And can we do it again?

It starts with a vaccine.

In the late 1700s, a scientist named Edward Jenner

developed a brand new way to fight smallpox.

He called it “vaccination.”

Before this point, the only way to gain immunity from smallpox was to catch it:

either through misfortune, or on purpose.

Jenner's method was far less dangerous.

Word of the vaccine spread quickly.

Within five years it was in the Americas.

Within ten, it was brought to Asia.

Vaccination alone would eventually be enough to drastically reduce cases.

And that's partially because of how smallpox is spread.

Unlike a disease like malaria, which can spread to humans from mosquitoes;

or Ebola, which can spread to humans from bats and other animals;

smallpox could only be spread to humans from other humans.

There were no animal vectors.

Which means vaccinating people would slowly eliminate the only way it could spread.

By the early 1900s, most of Europe, the United States, and Canada

had nearly wiped out smallpox.

But countries with fewer resources, civil unrest, or higher population density

struggled to effectively vaccinate and contain the virus.

And as long as smallpox existed somewhere,

it was a threat to people everywhere.

True eradication would require a global effort.

"Within the framework of the United Nations, a new organization exists

to promote the welfare of all people:

the World Health Organization."

In 1967, the World Health Organization established a unified plan

to eradicate smallpox once and for all.

Having a centralized agency changed the game for public health.

Nations pulled together, and vaccination campaigns spread around the globe.

Initially, the goal was simple: vaccinate everyone.

But that proved harder in densely populated places like India,

where it was hard to track outbreaks and the virus could spread quickly.

In 1974, over 15,000 people in India died of smallpox in the span of five months.

So the World Health Organization proposed a more targeted approach:

Instead of trying to vaccinate everyone at once,

public health officials focused on infected individuals,

using a form of contact tracing.

Doctors and volunteers would isolate the person

and vaccinate anyone who had come into contact with them --

and then, whoever had come into contact with those people,

effectively creating a buffer of immunity between the infection and the rest of society.

This was called “ring vaccination.”

It worked. Really well. Not just in India, but around the world.

And on May 8th, 1980, the World Health Organization declared smallpox eradicated.

These are the four factors that helped us eradicate smallpox.

And while there's no single path to disease eradication,

if one or more of these can't be met, it will make it much harder, if not impossible.

So let's talk about Covid-19.

Vaccines aren't the problem.

New technologies have brought us effective and safe vaccines in record time.

The issue with Covid-19 is the way it spreads.

Let's start with animal vectors.

Researchers believe the SARS_CoV2 virus originated in bats,

which means there's a way for it to spread from animals to humans.

So, even if we were to completely remove it from the human population,

it could reappear, just as it did the first time.

But the way it spreads from human to human is also a problem.

A person with smallpox could only spread the disease if they were showing symptoms.

But a person with Covid-19 can be contagious days before that point.

Some people never develop symptoms at all.

It's much harder to effectively trace something you can't see,

or isolate a person who doesn't even realize that they're sick.

And then there's this.

From the beginning of the pandemic, many countries have taken a nationalist approach to it.

Some countries banned exports of protective gear,

some countries restricted the export of vital drugs,

and the United States pulled funding from the World Health Organization.

In a September meeting, the UN secretary General said,

“The pandemic is a clear test of international cooperation –

a test we have essentially failed.”

Even as vaccines became available, richer countries are buying up the supply,

leaving poorer nations behind.

And that's a big problem,

because leaving the virus to spread unchecked in these other places

gives it more time to spread,

which increases the chance it will mutate.

Variants of the virus are already popping up,

and that leaves the whole world at risk.

All in all, Covid-19 is just not a good candidate for eradication.

But eradication isn't the only option.

Smallpox is the only human disease we've ever eradicated.

It's much more common for us to contain and control a disease.

And that's where many researchers think we'll land with Covid-19:

we'll vaccinate, and manage.

Lockdowns and quarantines will end,

and we might end up with a virus that we manage with an annual vaccine,

like the flu.

Or, something even more mild:

As more adults and vulnerable populations build immunity,

it's possible Covid-19 will become "endemic":

always around, but rarely developing into anything more than a common cold.

It's not the best answer.

But it's a reality we'll learn to be comfortable with.

We'll be able to go back to the way things were before.

But we shouldn't.

Eradicating smallpox took a colossal effort:

centuries to create effective vaccines,

and then decades more to build the framework needed for global campaigns.

It's a reminder of what we're capable of as a society.

But it's also a warning:

Covid-19 is far from the worst disease nature has to offer.

And this pandemic has shown us that we're not ready for something worse.

Because our failure isn't that we can't eradicate Covid-19;

it's that we let it rise to pandemic proportions to begin with.