[ Clock ticking ] -If you were born in 1900, you could expect to live on average just 32 years.

Today, global life expectancy is more than twice that.

It's one of the greatest achievements in human history.

♪♪ -This is the story of the ideas that have in the space of just a century or two changed what it is to be us by transforming the kind of lives we might live -- no longer short and under the shadow of disease, but healthy and long.

I'm David Olusoga, a historian.

I have to say, it does look like the sort of laboratory you see in the "Frankenstein" movies.

-And I'm science writer Steven Johnson.

-The average Black American lives three and a half years less than the average American.

-That to me is just really shocking.

-We're investigating the forgotten heroes of global health.

-The scientists, doctors, researchers and activists who touched billions of lives.

One of their most revolutionary ideas is vaccination -- defeating devastating illnesses with the jab of a needle.

Today, as the world grapples with another deadly pandemic, we reveal how vaccines became one of the most powerful tools we have in the fight for extra life.

♪♪ ♪♪ ♪♪ -David's in the U.K. and I'm in the U.S. With travel restricted right now... David.

-How are you doing?

-...we're connecting online.

I'm good.

You know, David, just by coincidence, I got the first dose of the COVID vaccine just two days ago.

And as I was sitting there waiting to get the shot, I just found myself thinking of all that ingenuity and knowledge and hard work, summed up and jabbed into your arm and giving your body this new protective power that it didn't have before.

-It reminded us that we are the recipients of a medical revolution or a series of medical revolutions that we had been taking for granted.

-I think of it is almost like a kind of invisible shield.

And vaccines are a big part of it, but the whole infrastructure of public health and medicine that has been quietly extending our lives for the last two centuries with increasing success.

And the one advantage, if "advantage" is the right word for it, of a pandemic like the one we're living through is it suddenly that invisible shield is visible.

And the need for that suddenly becomes very urgent.

-When the pandemic began, we very quickly assumed that medical science will be able to come up with a vaccine.

We were able to make that presumption because we are standing on the shoulders of heroes, pioneers in medical science and public health, whose stories we just don't know well enough.

-And if we don't look to that history to figure out what we did right to inspire us to to continue in that tradition, we'll be making a terrible mistake.

And there's something nicely symmetrical in a way, about the focus we have today on vaccines in trying to get ourselves out of this global pandemic.

Because if you go back and look several centuries to the origin point of this expansion in human lifespan, there are vaccines right at the beginning of that story.

Imagine it's 1856 in New York City.

Almost nothing you see behind me would have existed except for this one building.

A ruin today, it was New York's first hospital dedicated to treating people with smallpox.

Imagine what this place would have been like when it was filled with the sick.

And smallpox is a terrifying disease.

First you develop a rash, then these pustules form all over your skin that can swell and burst, scarring you for life.

Smallpox can cause blindness and kills around 3 in 10 who catch it.

Known as the Speckled Monster, it had ripped through Europe for centuries, killing rich and poor alike.

From the late 1600s, it devastates one royal family after another.

[ Clock ticking ] Many of the 400,000 people dying every year are young children, making average life expectancy tragically low.

-If there was any disease that must have felt like a sort of curse on humanity, it's smallpox.

And it was ancient.

There's evidence of it on -- on mummies from ancient Egypt.

This disease, its imprint in human history is just enormous.

-It's appropriate, in a way, that the very first medical intervention that made a difference really in human lifespan was developed precisely to combat this ancient threat.

♪♪ -It's around 1700, and Africa is in the grip of smallpox.

But some on this continent know how to protect themselves from this killer, and one man would carry this knowledge on a journey that would eventually lead to vaccination.

Well, we don't know where in Africa this man came from.

We do know what happened to him.

We know he falls into the hands of slave traders and he's trafficked across the Atlantic Ocean, just like millions of people between the 16th and the 19th centuries.

Eventually, he ends up in Boston, Massachusetts.

We know that in 1706, he was purchased by the members of a Puritan congregation of a Boston church.

And those parishioners gave him as a gift to their minister, Cotton Mather.

♪♪ Mather forces this young African man to take on a new name.

He calls him Onesimus, after the story of an enslaved man that appears in the Bible.

Much of what we know about Onesimus comes from accounts that Mather wrote, including a record of a conversation between the two men that would change Mather's life and the lives of many others.

Now, this only gives us an account of that conversation from Mather's point of view, but what he tells us is that he asked Onesimus whether he ever had the smallpox and Onesimus answered yes and no.

And then he went on to explain that he had undergone an operation which had given him something of the smallpox and that would forever preserve him from it.

Onesimus had been through an African procedure that was unknown in the West.

An incision is made in the skin and a tiny amount of fluid infected with smallpox is smeared into the cut.

This deliberately causes a mild illness, but crucially, it protects against a more deadly, full-blown smallpox infection.

It's called variolation, and it is the forerunner of vaccination.

It is risky.

Around 2% of people who undergo the procedure will die.

But even so, it is still far less dangerous than catching smallpox itself.

So this is an African, an enslaved man, somebody who occupies the very lowest position in colonial American society at a time when Europeans were confident that they were superior to Africans.

And what he's saying is that him and his people possess the knowledge to protect them from what was then one of the most dreaded of all diseases.

Boston 1721 -- a British ship arrives carrying smallpox, starting a major outbreak.

As the disease grips Boston and the death toll begins to mount, Mather launches a campaign to try to promote the idea of variolation.

But the public and much of the medical establishment are resistant to the idea of deliberately infecting people with smallpox.

And they are dubious about medical knowledge that comes from Africa.

Tensions rise to such an extent that a bomb with a message attached to it is thrown through Mather's window.

-"Cotton Mather, you dog, damn you!

I'll inoculate you with this: with a pox to you!"

♪♪ -The bomb, luckily, does not explode.

As smallpox rages through Boston, more than half the population are infected and 850 people die.

But Mather persuades a small number to undergo variolation, and among them, the death rate drops to around 2%.

One of the difficulties people have with it in Boston in the 1720s is that even in the midst of an epidemic with people dying, there is a resistance to the idea that knowledge that is from outside of Europe is illegitimate, and the most illegitimate of all forms of knowledge in the minds of a slave society in 18th century colonial America is knowledge from Africa.

-The other concern is 2% of people who were variolation just died from the procedure.

Now, that was still better odds than risking getting smallpox out in the wild on your own.

So it was still the logical thing to do.

But however much it might have made sense, there was something fundamentally repulsive about the idea of taking someone, particularly a young child, potentially your child, and deliberately infecting them with the pus from such a deadly disease.

-No one knows where variolation began, but there's evidence of similar practices in China and India since at least the middle of the 16th century in the early 1700s, awareness of variolation was growing across the West.

Not long after Mather learns about it from Onesimus in Boston, a British aristocrat comes across it on the other side of the world.

Lady Mary Montagu was brilliant and beautiful and witty, and she could easily have spent her entire life in the social playground that was Georgian London, but she rejects the husband that her father selected for her, and she instead marries a man who just a few years later is appointed ambassador to the court of Ottoman Turkey.

Lady Montagu's brother had died from smallpox and she had been badly scarred by the disease.

So when she encounters variolation in Ottoman Turkey, she is captivated.

In a letter to a friend, she describes parties in which guests are deliberately exposed to smallpox, making the disease entirely harmless.

Lady Montagu decides to variolate her five-year-old son.

The smallpox infection grows on Edwards arm, but he survives and never catches the full-blown disease.

By 1721, Lady Montagu is back in England.

As smallpox sweeps London, her daughter Mary is variolated and thrives.

It catches the attention of Lady Montagu's influential friends and her most influential friend is Princess Caroline, the wife of the future George II, and she is persuaded, despite the opposition of her father-in-law, George I, to have two daughters variolated.

Princesses Amelia and Caroline both survive and they never catch smallpox.

And that is the tipping point.

Royal endorsement is what allows the practice of variolation to take off in Britain.

What this story of Mary Montagu demonstrates is that for an idea for a new medical technology to be transmitted from one society to another, it matters not just that the idea has some efficacy, that it works, but it matters who is the person doing the transmitting because Mary Montagu is Lady Montagu, and that's really significant.

So that's not really an issue that this idea has come from Ottoman Turkey, from Islamic Turkey, from outside of Europe, because the person delivering it, the person advocating for it, is one of the elites.

She's one of them.

-And that circulation of that idea made a really crucial difference in the history of human health, because for the first time in the second half of the 18th century, you see among the elite of England, increasing lifespan in a linear fashion, a line going upwards.

That had never really happened before.

But at the same time, you see for the first time a gap in outcomes between the wealthy members of society who are living longer lives and the rest of the country, which is still stuck at that median of 35 years where human beings had lived for the history of civilization.

It's both the beginnings of the great escape into longer life and the beginning of health inequality.

-Nearly 40 years after Lady Montagu brought variolation to Britain, an eight-year-old boy is variolation in Gloucestershire.

He will grow up to be a doctor who will change the world.

His name is Edward Jenner.

This is Edward Jenner's study, and it was right here that he wrote this book about his scientific work, and in it he tells us that in May 1796, he met a milkmaid named Sarah Nelmes, and she had contracted cowpox and a huge sore, a pustule, had developed on her hand.

Now, Jenner is so interested in this that he includes this drawing in the book showing the sore on Sarah's hand.

[ Cow moos ] Milkmaids catch cowpox, a mild skin disease, from the udders of infected cows.

But they rarely catch smallpox and they're famous for having unblemished faces.

This sets Jenner thinking -- perhaps catching cowpox prevents milkmaids from catching smallpox.

And that led him to develop a theory that it might be possible if you infected somebody with cowpox to protect them from smallpox.

If it works, it will be far safer than variolation, which exposes people to a deadly disease.

Jenner tests his theory.

The piece of medical equipment that Jenner uses is this.

It's a lancet, a sharp blade.

And this one was actually owned by Edward Jenner.

What he did was he cut into the pustules on the hand of Sarah Nelmes and he extracted some of the fluid inside.

The next thing he needs to do is to find someone to be the subject of this experiment, and he chooses somebody close at hand -- James Phipps, the eight-year-old son of his gardener.

Jenner took the lancet and he made two small incisions into the boy's arm... ♪♪ ...and smears some cowpokes fluid into the cuts.

♪♪ Over the next days, Jenner observes the boy's arm as the mild cowpox infection develops.

♪♪ Six weeks later, Jenner moved on to the next and far more dangerous stage in his experiment.

He cuts James again.

This time he smears smallpox into the wounds.

Amazingly, he develops no symptoms of the disease.

Jenner's new vaccination method is safer than variolation.

Exposure to a mild disease, cowpox brings protection against the biggest killer of the age, smallpox.

-The Jenner story is a classic.

I mean, it's one of the few stories of scientific breakthrough that you will actually read in a traditional history survey of the modern age.

But there's something kind of misleading about it in a way.

Yes, the vaccine is an important breakthrough, but it was clearly building on this longer history of variolation.

He was modifying and refining an existing idea that had a much, much longer history.

-Smallpox is always there.

It's always on humanity's shoulder.

And it's not surprising that this global disease, this technology to address it, was one that spread around the world in exactly the same currents as the disease -- trade, empire, migration, movement.

-And the thing that's fascinating about Jenner's work here, for all of his brilliance, he fundamentally doesn't understand how the immune system works, right?

No one does at that point in our history.

But today, we actually do understand all of that.

We have a much richer comprehension of the body's immune system, and that is enabling us to design a whole new class of vaccines that would have exceeded anything in Jenner's imagination.

♪♪ Dr. Kizzmekia Corbett worked on one of the new generation of successful COVID-19 vaccines.

Walk us through what happens when a virus like the coronavirus enters our body with some drawings.

-Yeah, so viruses are these very small objects.

It's drawn pretty big here, but they're essentially kind of circular objects with a little spike proteins sitting on the surface.

And its entire job is to get inside of a cell so that it can replicate.

So eventually what comes out of the cell are new viruses that are the daughters of the original virus.

So this entire reaction actually causes the body to make an immune response.

-First, the body figures out how to fight the virus.

Then the immune system forms a memory of what worked.

So if you get infected by the virus again, your body can fight back quicker.

Vaccines mimic this process.

-It is to show the body something that's not a virus or at least not a full-blown virus that might be able to replicate and cause disease, but to teach the body and the immune system about what that virus looks like.

-Right.

-And then when it sees it again, it is able to respond very quickly.

-So it's a kind of training of the immune system.

-Immune system boot camp.

[ Laughter ] -Exactly.

Classical vaccines work by taking the original virus and making it harmless in the lab before injecting it into people.

But some of the new coronavirus vaccines work in a totally different way.

-Scientists have got really creative.

The body doesn't need to see the entire virus, but only maybe a piece of it so that it recognizes that virus later.

-The coronavirus is covered in spike proteins.

It contains the genetic code to make them.

Now, what's so clever about the vaccine Dr. Corbett helped develop is that it uses just that tiny bit of code... ...to tell the cells in our body to make copies of only the spike proteins.

These spike proteins then trigger an immune response.

♪♪ -The beauty of it is your body remembers that spike protein in such intricate detail that it's able to see the spike protein on a virus later and potentially prevent infection.

-What it recognizes are these telltale properties of the virus.

-Right.

When a new virus comes along that looks like that virus, the immune system knows immediately to fight against that virus.

-I love this transition from, you know, developing these huge vats of inactivated virus to deliver in the form of vaccines to basically a software download.

-That's exactly what it is.

You are sending a code and it really allows you to move very quickly in the case of an outbreak or a pandemic like we're having right now.

-Yes, that's so powerful.

-I think it's probably one of the most powerful tools that I'll ever experience in medicine ever in my lifetime for sure.

-One of the key breakthroughs behind the coronavirus vaccines is the speed with which we can now learn about new viruses.

Just weeks after the virus was first identified, we were sharing its genome around the world.

-Hello.

Good morning.

Good morning.

Good morning.

Most people see me as the bespectacled old grandpa.

That's the new thing.

Before, I was the vibrant young director and now I'm the bespectacled old grandpa.

That's what the newspapers have designated me.

-[ Laughs ] So much of the progress that we've seen, the development of the coronavirus vaccine, has come from that rapid sequencing of the genome.

Is that true?

-If I were to have told my mentors back then that, guess what, you don't even need to get the pathogen in your hands to make a vaccine...

So, you know, the old vaccinologists of back in the day, as it were, would have laughed at you.

"What do you mean?

How can you make a vaccine if you don't have the pathogen?"

Well, all you need is a computer screen.

And the first sequencing of pathogens back not too long ago would take over a year to do.

You can do it now, essentially in a day.

You could just, bingo, you've got it.

So, in the case of COVID-19, as soon as the Chinese put up on the database, the public database, the gene, we knew in a microsecond that that gene codes for the spike protein.

So you pull out the gene, the sequence, I mean, in silico, in the computer.

-It's software.

-It's there.

It's software.

You pull it out and you stick it into whatever your vaccine platform is and the body sees it, makes an antibody response.

That's it.

You're done.

That is just such an extraordinary advance in vaccinology right now.

It's completely different than it was years ago.

♪♪ -We're back in the early 1800s.

Edward Jenner's new vaccine has just arrived in Boston.

Now, the next part of this story is crucial.

It's all about how vaccines went from being just a scientific discovery to actually changing people's lives.

♪♪ A Harvard doctor named Benjamin Waterhouse is on a mission to bring Jenner's vaccine to America.

He starts writing to influential people.

One of them is an amateur scientist in Virginia who asks for some of this amazing new vaccine.

He wants to test it on hundreds of people.

And what makes this story even more astonishing is that amateur scientists real job was president of the United States and his name was Thomas Jefferson.

From the start, Jefferson sees the world-changing potential of the vaccine.

He writes, "Every friend of humanity must look with pleasure on this discovery, by which one evil, the more is withdrawn from the condition of man."

And this is really almost a utopian vision of the future, not just focusing on protecting individuals, but in fact, in ridding the entire world of a disease.

Jefferson begins his vaccine trial on his estate at Monticello, but his approach is ethically disturbing.

First, he tests the vaccine on some of the 130 people he enslaved.

Then he moves on to his family and neighbors -- around 200 people altogether.

Medically, the trial is a success.

When he exposes some of the vaccinated people to smallpox, none of them get sick.

This is really the quintessential Jefferson moment, I think.

It's capturing the very best in him and the very worst in him.

I mean, here you have this groundbreaking moment in the history of human health and he's performing this experiment, pioneering science.

But he chooses to experiment first on those who can't object because they've been enslaved.

This is an important part of this early history -- ideas that are getting into circulation that will ultimately be progressive ideas and extending our lives are initially bound up in these very reactionary exploitation of the powerless in society.

It's a huge part of that story.

-No matter what hopes or aspirations Jefferson might have had for vaccination, you can't get past the fact that he experimented on enslaved people that he himself owned.

And it's an example of these really, really uncomfortable power imbalances in the history of early medical trials.

It's like Jenner with James Phipps, a boy from a poor background.

His father works for Jenner.

This is just a more extreme example.

-There's another element... to power in the story, and that's the fact that Jefferson was president of the United States while he was doing these trials, and that in a way, is quite extraordinary to think about in the context of modern, particularly American politics.

But I think if there's a lesson from the coronavirus pandemic, it's that our leaders need to be versed in health and medicine and science.

And that's one part of the story of the founding fathers -- for all their attitudes that are now abhorrent to us today, that interest in science and that interest in new ideas in medicine is something I hope we can learn from.

♪♪ -Within a few years, Jenner's vaccination method spreads across the world, carried by a growing network of doctors and scientists.

♪♪ Today, new global networks are ramping up to distribute coronavirus vaccines on a scale far beyond anything previously attempted.

-The challenge of the COVID vaccine delivery is immense.

Everybody in the world is going to need to get a COVID shot.

-We're good to go.

-The scale is enormous.

There have been forecasts that have shown potential of up to 8,000 747s just for vaccine delivery globally.

-Vaccinating the planet isn't just a logistical challenge.

Dr. Jeremy Farrar runs Wellcome, a global health foundation working to ensure fair access to COVID vaccines.

-We have the vaccines, but now we need to make sure that these are available to everybody in the world.

From my perspective, this is a public health imperative.

It's a moral, it's an ethical imperative, but it's also enlightened self-interest.

-Wealthy countries are way ahead in the scramble for vaccines.

They've invested billions making sure they get enough doses to vaccinate their populations, sometimes several times over.

Low income countries are a long way behind.

-If we vaccinate everybody in some countries and very few people in other countries, it will prolong the pandemic and we run the risk that there will be new strains of this virus which evade treatments and evade the vaccines.

And those will then spread around the world.

And so we'll go from pandemic to pandemic, if you like, reverberating around the world maybe for years to come.

So the fastest way to end this pandemic is to make these vaccines available everywhere in the world in an equitable way.

-Most rich countries are supporting a scheme to provide two billion doses to poorer countries, but more money is needed.

-I'm very optimistic that if the world chooses to, it can manufacture vaccines at scale, it can distribute those, and it can do so to every country on Earth.

What I'm much less optimistic about is the speed we need to do it, whether we will deliver that.

It won't happen by chance.

It will only happen, in my view, because people push it and because people make the right choices.

♪♪ -The journey from Edward Jenner's first vaccination to rolling out COVID-19 vaccines across the planet is not only a story of scientific breakthroughs, but also of trust.

Today, noisy anti-vaccine movement on social media shows us that vaccination can't be taken for granted.

Much of it is promoted by influential anti-vaxxers or any-vax groups, all of it exploiting the emotional intensity of the Internet.

♪♪ -You might think that this is a new phenomena, but in fact, anti-vaxxers are as old as vaccines themselves.

By 1802, Jenner's discovery is inspiring ridicule and anxiety.

Over the next 50 years, vaccination saves lives.

It helps to cut deaths from smallpox in London from 88 in every 1,000 to 16 in every 1,000.

But many poorer people in Britain are not getting vaccinated.

So the government makes the procedure mandatory for children under three months.

The new law sparks a backlash and influential dissenters, like the alternative healer John Gibbs, take up their pens.

This is one of his responses to the Vaccination Act.

It's a pamphlet called "Compulsory Vaccination Briefly Considered," although at 90 pages long, this is not exactly what I would call brief.

Gibbs wages his battle against vaccination on grounds that were very new in the 1850s but that feel very familiar today.

What Gibbs argues here is that people have what he calls a natural disgust to the idea of transferring to the veins of their children a loathsome virus derived from the blood of a diseased brute and that people cannot bring themselves to believe under any circumstances that the true way to health and longevity can be to corrupt the blood.

So he's playing on a very deep and emotional arguments about the sanctity of the body and the purity of the blood.

But these are also philosophical arguments about the sovereignty of the individual over their body.

Now, this pamphlet was written in the 1850s, and yet a lot of the arguments it contains and this level of emotion about vaccination feels really familiar to us today.

And that's because these are many of the same arguments that are used today by the anti-vax activists.

♪♪ ♪♪ -The story of human health is always a political story on some level -- a story of political struggle, people fighting for the adoption of these new lifesaving approaches.

And we're still living through that same kind of political landscape today with the coronavirus.

And yet the irony right now, the tragic irony, is that some of the communities where there is the most vaccine hesitancy or vaccine resistance are precisely the communities -- like the African-American communities in the U.S. and ethnic minorities in the U.K. -- precisely the communities where the coronavirus has hit the hardest.

-And that task of building trust is made even harder by online misinformation.

Now, that affects everybody, but those who are spreading online misinformation to African-American communities and minorities in UK and Europe, they are able to point to real historical incidents when Black people were the subject of unethical medical trials.

Doctors in the United States have reported African-Americans having hesitancy towards the vaccine because they know about something called the Tuskegee Trials, which was a medical trial, an unethical trial, on African-American men who were suffering from syphilis.

It started in the 1930s, and it involved hundreds of African-American men in Alabama in the south of the U.S.

They were denied treatment for syphilis when they were told that they were being treated, when actually they were being observed.

That led to deaths.

It led to the destruction of families.

And it was only uncovered in the 1970s.

It's very much within living memory.

And we shouldn't forget also that in April 2020, just a few months into the COVID-19 pandemic, two French doctors suggested that we could carry out trials on new vaccines for COVID in Africa on Africans, as if Africans were sort of legitimate guinea pig.

So there's a history here which can be weaponized by those selling misinformation, which can make the situation even worse.

-My body, my choice!

-My body, my choice!

-My body, my choice!

-Suspicion about vaccines undermines vaccination programs.

Not long after 9/11, an international effort to vaccinate more than 50 million children against polio in West and Central Africa hit a problem in northern Nigeria.

As the vaccination program ramped up in Kano, a predominantly Muslim state, a rumor started to spread.

-I heard one community member in one of my community discussions say, "It says clearly on the box 'sterile.'

They're trying to sterilize us."

And it was something I would have never thought of, but that was the level of suspicion and angst about, you know, the imposition of this.

-So, they thought this was a Western plot to -- to sterilize the people, the Muslim population of northern Nigeria.

-Absolutely.

-And this rumor gained traction?

-It gained traction to the extent that the governor of the state, the political leader of the state, whether or not you wanted a vaccine, he banned it.

-The virus spread to 20 previously polio-free countries across Africa and as far away as Yemen and Indonesia.

The boycott ended after 11 months when vaccines were sourced from a Muslim country.

This is not just places like Nigeria, places in the developing world.

These rumors happen and can start anywhere.

-Anywhere.

It's throughout both poor and rich countries.

And this notion that people believe rumors because they just don't know any better is absolutely wrong.

Whether it's rumors and conspiracies in London or Manchester that 5G towers are causing coronavirus, or in the US, that the new vaccines are going to alter your DNA, these are circulating because people have a deep distrust.

If you distrust the government, if you distrust big business, you're going to think twice and you might be much more vulnerable to a conspiracy.

-What tools do people have to try to persuade people that these rumors are exactly that, just rumors?

-Well, I think in a way, the public health community has focused too much on persuasion.

I think that we're not doing enough listening because people have anxieties.

They have concerns, and unless we address them, they're going to come and bite you back, as it were, as happened in Nigeria.

-Understanding the history of vaccine programs, understanding how they run into trouble, how they can go wrong, why they go wrong, that's never been more important because we are literally facing the task of vaccinating everyone on the planet, eight billion people, to protect them from COVID-19.

So the history is full of answers to problems that we're about to face.

-And we can look to that history for stories of success as well.

And maybe the most inspiring story of all involves a mass vaccination effort at extraordinary scale.

And fittingly, it all revolved around the disease that launched vaccines in the first place, smallpox.

♪♪ It's May 1958, the height of the Cold War.

We're in Minneapolis, Minnesota.

♪♪ The Soviet deputy health minister calls on member states of the World Health Organization to come together to eradicate smallpox, which is still killing around two million people a year, mostly in poor countries.

A decade later, the United States and the Soviet Union are among 73 countries working together to vaccinate the planet.

I'm talking to someone who was a part of that mission.

Larry, it's good to see you, my friend.

-Wonderful to see you, Steven.

Thanks for coming all the way to my living room.

-[ Laughs ] I'm sorry we're not in person.

Fresh from medical school, Larry Brilliant joined the WHO in India in 1973.

The head of the Centers for Disease Control's Smallpox Eradication Program, Dr. Bill Fahey, took Larry to see his first case of smallpox.

-I remember this little girl who was just covered with scabs and lesions that were not yet scabs.

She was so sick, and it was that poignant moment of seeing this horrible disease, that this wasn't even the worst case.

And I said to Bill something idiotic, like, you know, "Can we call an ambulance?

Do we take these children to the hospital?

What do we do?"

And Bill said to me, "There's no cure.

There's nothing that we have that we can do for these children other than eradicate this disease."

Far more people thought it was a fool's errand than thought it could ever happen.

-What were the most serious roadblocks from making something as ambitious as smallpox eradication a reality?

-How do you find every single case of smallpox in a world of billions and bring the vaccine to every village?

We wound up making in India alone nearly two billion housecalls.

That scale required an army of over 150,000 just in India -- the largest peacetime U.N. army of its time.

♪♪ -The eradicators' job was made even harder because smallpox was flourishing in some of the hottest countries in the world.

-The smallpox vaccine originally would die in the heat.

If you have a vaccine that requires refrigeration, you could only vaccinate where there was electricity, which meant in the urban centers.

The idea of taking the vaccine and taking it out into the villages seemed a road to far until two tremendously innovative things happened.

-First came freeze drying, a technique developed in the 1950s by British virologist Leslie Collier.

-And just like coffee, if you freeze dry something and then reconstitute it with water, you can avoid having to refrigerate it.

And you can then also manufacture the vaccine in countries all over the world, which is what we did with smallpox.

-Then the cumbersome jet injectors that had been used to vaccinate people were swapped out for a radical new type of needle.

In the 1960s, an American microbiologist named Benjamin Rubin took an ordinary sewing needle and ground down the tip of it, creating this -- the bifurcated needle with its distinctive double pronged fork shape at one end.

Dipped into the vaccine, the two prongs held just the right dose.

This simple needle turned around 150,000 villagers into vaccinators.

♪♪ Despite all these innovations, vaccinating everyone in a country was proving impossible... until Bill Fahey came up with a brilliant idea.

It was a late 1960s, and he was running out of vaccine in Nigeria.

-He asked himself, "What is the most ethical way to allocate the vaccine?"

You don't just give it to everybody in line.

He decided that you give it to the people who were the most susceptible, the most vulnerable, who might get it next.

And who were these people?

Well, they were the people who were family members or neighbors of people who already had the disease.

-It became known as ring vaccination, and this is how it works.

Let's say these blue chips are the population of a country or region.

Each chip represents a person.

Let's say each red chip represents one smallpox infection.

Once you know where the infections are in the community, you can target your vaccine, only vaccinating the neighbors of the people infected, protecting the most susceptible to the virus.

You're building up a ring of protection around the virus, turning it into a predator with nowhere to go.

The effect was immediate.

Cases in India fell from 188,000 in 1974 to just over 1,400 in a year.

From the start of the program in 1967, smallpox was eliminated in one country after another until in 1975 just one pocket of virulent smallpox remained in Asia -- Bangladesh.

♪♪ Larry was sent to investigate.

-I set up a search of the whole area of all those islands in the Bay of Bengal, and the only case we found was this one girl, Rahima Banu.

-Larry went to meet her with a colleague.

-We both cried when Rahima Banu coughed the last time.

and the viruses that were in her lungs fell on the hot plains of Kuralia Village and were cooked by the sun or the scabs fell off and she survived.

But when the scabs were incinerated by the heat, that was the end of an unbroken chain of transmission of Variola major going all the way back to Pharaoh Ramses V. That virus that history has written about so many times that ravaged medieval cities, that killed 30 kings and queens and emperors... that disease was gone in that moment with that young girl.

That, to me, was the moment that history celebrates as the end of an unbroken chain of evil.

-It's estimated around 300 million people died from smallpox in the 20th century, more than three times the number killed in the two world wars.

And then...none.

Wiping out smallpox has helped raise average life expectancy in low-income countries from 42 years when the effort began to more than 60 today.

One of the things that I think is so important as a message for us now in the current crisis we're in is the extent to which smallpox eradication was a story of global collaboration, right?

-Oh, I think like climbing Mount Everest, perhaps the difficulty attracted some of the most amazing people in the world, people from 200 different countries, 20 nations sending doctors of every faith -- Muslims, Hindus, Buddhists, Jews, Christians -- all working together, people of every color, the Russians and the Americans burying the hatchet to come together and collaborate.

In the middle of a moment in time, Steven, when we had 20,000 nuclear weapons poised facing each other, we still managed to work together to eradicate smallpox.

I think people forget what human beings can do when we're unencumbered by divisiveness and hate and that we stand up to the moment in time.

♪♪ -What I find so inspiring both about smallpox eradication and the current efforts to fight COVID-19 is that, in a sense, it has always been a global story.

From the beginning with variolation, it was a story about an idea traveling around the world without respect to borders, without respect to nationality.

And that story of progress is inspiring.

But the other thing about it is that it's not inevitable and it's not necessarily going to continue.

I mean, we are talking in the middle of the most significant global pandemic since 1918.

And in the United States, we are going to see the most dramatic drop in average life expectancy in one year since that period.

And so we may be at the edge of seeing all of that progress grind to a halt.

-And in that scenario, the story of smallpox becomes one of the most powerful stories that we can celebrate and tell ourselves, because that is the story of what can be achieved, what can be achieved if governments work together, if agencies like the WHO are able to mobilize hundreds of thousands of people on the global level.

We have to find strength in that story because we can't allow any complacency to revive itself.

We need to empower the agencies.

We need to push Big Pharma to take their role in this, their responsibility and not put profits first all the time.

And we need to see this as the blueprint for global cooperation.

-And we know that there are a whole host of other ancient threats that are still out there, these diseases that continue to kill millions.

And we know we have the power on some level to, if not fully eradicate them, then greatly diminish their impact.

So the question is, do we have the will?

Do we have the confidence?

Do we have the ability to work across borders to solve those problems the way we solved the problem of smallpox?

♪♪ ♪♪ -Today, as the world grapples with another deadly pandemic, we reveal how drugs became one of the most powerful tools we have in the fight for extra life.

-This is the groundbreaking moment -- penicillin.

-Do you think we're heading towards one pill for any virus?

-That would be really nice to have.

-Using artificial intelligence, the progress against these diseases is going to be tremendous.

-I'll give you the biggest story in human history -- how we doubled our life expectancy.

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