-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 a Frankenstein movie.

-[ Chuckles ] 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 revolutionary ideas was fighting disease, not with vaccines and drugs, but by persuading people to alter their daily routines.

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

♪♪ ♪♪ -I'm in the U.S., and David's in the U.K. -Sound, take one, day two.

-With travel restricted at the moment, we're meeting online.

Better mask here.

I remember walking through the streets of New York City in March of 2020 and seeing these sidewalks that are normally so teeming with people, and they're just empty.

No one's there.

And I remember thinking at the time that this was an experience that was happening all over the world, all of these extraordinary changes in behavior that, when you sum it all up, is probably the single most concentrated and immediate transformation in human behavior on a global scale ever experienced in the history of this planet.

-And perhaps understandably, there were no shortage of people saying that this was all impossible, that this couldn't happen, that you couldn't possibly shut down high-tech, industrial, 21st century societies, that people wouldn't accept lockdowns.

And I think what it showed is that, at times of real stress and real threat, we are surprisingly able of adaptations, of making changes to our lives that in normal times we just -- would be unthinkable.

-And that kind of behavior change has actually played a huge role in the expansion of life expectancy over the past few centuries.

We tend to celebrate the vaccines and the magic-bullet drugs, but there's also a crucial part of that history that involves just ordinary people, you and me, making changes to our lifestyles.

♪♪ -One lifestyle change in particular... ...that made a huge difference in extending our life-span was the move to cleaner living.

Two centuries ago, big cities like London were unimaginably filthy.

The Thames was thick with sewage and streets like this were just covered in horse manure.

And along with the manure, household waste was just thrown out here and left to rot.

And the people were filthy, too.

With no running water in ordinary homes, washing was a luxury.

[ Bell tolls ] It seems obvious to us now that conditions like these were the perfect breeding grounds for disease, diseases that can kill in weeks, sometimes in just days.

As a Londoner in the 1800s, you'd be lucky to live beyond 35.

Many of the people who fell victim to these diseases were children.

Frank, aged 1 year and 10 months, died 19 August 1891.

John, aged 2 years, 2 months, died 14th of August, 1890.

Arthur, who died 19th of April, 1892, aged 14 days.

At the time, it was thought that diseases were spread through the air, and it took decades for those ideas to be overthrown and for people to understand that hygiene and sanitation was fundamental, critical to controlling the impact of disease.

♪♪ -[ Crying ] -Since then, there's been a revolution in the way we live... [ Babies crying ] ...that has transformed life expectancy... ...and it all began with a young doctor from Hungary called Ignaz Semmelweis.

In 1846, he lands the job of assistant physician at Vienna General Hospital, which has the largest maternity unit in the world.

[ Crying continues ] Not that long into the job, Semmelweis has a major problem on his hands and a mystery to solve, the hospital has two birthing wards, one staffed by doctors and the other by midwives.

[ Crying continues ] In the doctor-led ward, an alarming number of women are dying of a fever.

It kills at the most tragic of moments, shortly after childbirth.

How could two wards in the same hospital have such radically different death rates?

What I've always found so thrilling, really, about this story is that, on some fundamental level, it's a mystery, and that's what drives Semmelweis further and further into trying to understand what's happening.

-And you have to admire how methodical and punctilious he is with every variable.

He looks at the diet of these women.

He plots the deaths over the years so we can see if there's any seasonal variation.

But the one thing he doesn't do is the first thing that the modern doctor would do, which was to try to identify pathways by which these women might be becoming infected.

He doesn't do it because it's the 1840s, because it's before anyone understands that down the microscope is this empire of microbes and bacteria which are at the heart of disease and infection.

-It therefore doesn't matter to anyone that in between shifts in the maternity ward, the doctors go upstairs to the mortuary to dissect corpses and then pop back down to deliver more babies... ...without washing their hands.

Then, one day, a tragedy occurs, one of Semmelweis' colleagues cuts himself with a scalpel while performing a dissection.

He comes down with the same fever that's plaguing the first clinic and dies, and this really gets Semmelweis thinking.

Could it be that some kind of invisible particle is responsible for his colleague's death?

And were those same invisible particles being transmitted from the hands of the doctors to the bodies of the mothers?

To test his theory, Semmelweis proposes a radical intervention.

From now on, all doctors delivering babies in the first ward will have to wash their hands with a chlorine solution after dissections.

The results are irrefutable.

As soon as handwashing is introduced in the first clinic, death rates plunge by 90%.

♪♪ So this is the point where you might think science has solved the problem, everyone will adopt handwashing, and thousands of lives will be saved, but not so fast.

Semmelweis' ideas are rejected by the medical establishment.

He loses his job and winds up in a mental-health institution after suffering a breakdown.

♪♪ To me, David, the important lesson of the Semmelweis story is that [chuckles] having the data on your side, being a brilliant investigator, is often not enough.

-There's a social element to this story because it's also about who Semmelweis was and who he wasn't.

He is a junior doctor in an extraordinarily hierarchical society, in a very, very hierarchical profession.

He's the wrong person to be telling his profession full of grandees this quite difficult message that the cause of the death was something about them, even with that weight of evidence, even with women's lives being saved by that intervention.

-But I think it shows how people get entrenched in certain ideas, right?

There's actually a term for this, the Semmelweis reflex, right, which is the idea of just kind of rejecting out of hand some new proposition, because that's just not the way it was done.

When we look at the history of progress, you know, we traditionally look at it as a series of kind of breakthroughs and in leaps forward and when the brilliant idea happened and change the world.

But part of that history is also a brilliant idea that emerges and doesn't change the world.

-While Semmelweis is being ignored in Vienna... ...elsewhere in Europe, others are pursuing the idea that cleanliness saves lives.

♪♪ ♪♪ Everybody's heard of Florence Nightingale, the young British woman who, much against the wishes of her wealthy family, embarked upon a career in nursing.

And that decision led her in 1854 to the Crimean War, where she was in charge of caring for injured British soldiers.

When she returns home from the war, Florence is troubled by the unsanitary conditions she's witnessed in the Army hospitals, so she begins meticulously analyzing data on the causes of death for the thousands of British soldiers who've lost their lives in the Crimea.

And it confirms what she suspects, that disease has been killing them far faster than gunfire.

Disease, she believes, is caused by poor hygiene.

She then has an ingenious idea about how to present this data so that people pay attention to what's happening.

What she comes up with is this, the rose diagram, and it shows the number of soldiers who've died in the British military hospitals in the Crimea.

And each of these wedges, each of these petals of the rose, they represent a different month.

And each of these blocks of color represent the numbers of soldiers who've died and the colors, they represent the different causes of death.

So this pinky red color, that is the number of soldiers who have died of their wounds, black represents the number of soldiers who've died in the hospitals from other causes, but blue, that's the number of soldiers dying in the hospitals from infectious diseases.

And what we instantly understand from this diagram is that the big killer in the Crimea is disease.

Now, this other diagram offers some hope because what it shows is how, after changes to the sanitary conditions in the hospitals, the story begins to change.

And month by month, the number of soldiers dying of diseases in the hospitals begins to fall as the conditions in those hospitals are improved.

And by the end of the year, the number of soldiers dying from disease has fallen by 99%.

♪♪ Now, this diagram is not really what Florence Nightingale is famous for, but perhaps it should be because it was absolutely critical in getting across the fundamental key message that, in the Crimea, the British military hospitals have been deathtraps and that much of this death and much of this suffering could have been avoided.

[ Bell tolls ] -When you're trying to persuade people to change their behavior, how you make the argument is almost as important, if not more important, than the data behind the argument itself.

I mean, if you look at Semmelweis' argument that he makes for handwashing, you know, it's presented in the form of statistical tables.

I mean, it's just pages and pages of kind of raw numbers.

Whereas Nightingale does something very different, right, she converts all that data into these vivid diagrams.

-And she then uses things about herself to force the issue, to force the discussion.

She returns from the Crimea literally a living legend.

She's a national hero.

And she's a very difficult woman to say no to, and that's partly because of her personality, but she's also an aristocrat in a deeply class-based society.

So you have a combination of a powerful-minded individual who is a national hero and also a sort of genius with arguments and statistics.

-What also helps Nightingale's life saving ideas get noticed is timing.

Her work coincides with a period of intense scientific discovery.

The hygienic movement is seriously hampered by a centuries-old idea that all illness is caused by poisonous vapors, basically bad smells emanating from things like stinking trash and rotting meat.

But a handful of pioneering European scientists are starting to develop an alternate idea.

In Britain, Dr. John Snow challenges the centuries-old belief that all disease is caused by bad smells by proving that cholera spreads through dirty water.

Meanwhile, in France, scientist Louis Pasteur uses a powerful new microscope to identify invisible organisms in water that's been exposed to the air... ...prompting German scientist Robert Koch to discover just which of these germs are the most deadly.

All of this creates a tipping point, finally persuading the medical establishment that hygiene is the first line of defense against disease.

By the 1890s, doctors are routinely washing their hands and using antiseptic techniques in surgery.

Soon, ordinary people are being persuaded to clean up themselves and their homes, too.

There are calls from the influencers of the day to take a daily wash and a Saturday-night bath.

Everyone is going mad for soap.

♪♪ The tide begins to turn on deadly germs in Europe and the U.S., helping us gain an extra two decades of life in the first half of the 20th century, taking life expectancy to 62 years.

-But what is it about soap that's so effective?

Simple soap and water is enough to rupture and to kill some of the most deadly pathogens.

Soap rips pathogens apart like a crowbar, trapping the fragments in tiny bubbles that are then flushed away by water.

♪♪ And it works on all kinds of germs, viruses, bacteria, and dirt.

At the molecular level, soap breaks everything apart.

And what that means is that, at the level of society, it helps us to hold everything together.

-You think about the objects that made the modern world, right, and what naturally comes to mind are much more kind of high-tech machines, right?

But if you look at it honestly, if you look at the consequences for health and our life-span, you have to put the humble bar of soap on that list.

-You know, there was a certain amount of disbelief in the early months of the COVID-19 pandemic that the most important thing we could do was to use something that was just part of ordinary life that we all had in our homes.

-And yet, apparently, despite the pandemic that's raging around us, people still aren't washing their hands enough.

And so that gets to the question of, how do you persuade people to change their behavior, even if the behavior in question is something that is so easy to do, something so familiar as washing your hands?

And this is one of these places where, actually, we do have a very rich, nuanced, well-funded science of persuasion that's out there, which is the advertising business, right?

So the question is, can we take some of that persuasive power and use it to get people to change their behavior, to make themselves healthier?

♪♪ -Look them in the eyes, and tell them you're doing all you can to stop the spread of COVID-19.

Stay home, protect the NHS, save lives.

-[ Speaks indistinctly ] Today, advertising agencies employ behavioral scientists to help persuade people to make healthy lifestyle choices, and they've discovered key insights into how the human mind works when faced with a call to action.

-So there's something we call in psychology the intent-action gap.

And this is the gap between what we ought to be doing, what we say we're going to do, but what we actually do in practice.

And I think health is a really, really good example of this.

-So everybody knows that wearing a seatbelt, eating healthy food and not fast food, we all know that that's what we should be doing, we all know that's kind of what we want to do, but it's not what we do.

-Definitely.

Changing behavior is really difficult, and maintaining that change can be even harder.

And it's sometimes these kind of psychological barriers which stop us doing things that we know are good for us.

-Ella's team was recently approached by a client concerned about hand hygiene at a food factory in Guatemala.

-The factory workers weren't washing their hands properly or if at all.

They'd been given extensive hygiene training, and they had all their soap hand towels, and everything they needed to actually wash their hands, but nothing was making any difference.

And the microbiology tests were identifying that 4 out of 10 people had unsafe hands that could be deemed an actual threat to humans.

And what we did was we designed the hand-safety stamp, and it works by having a specialized sticky ink, which takes as long to rub off as it does to accurately wash your hands.

So, essentially, the workers had to arrive to the factory, and every single person was stamped as they entered.

And this provides a really visible symbol.

-So, suddenly, having dirt on your hands, which is dangerous if you're preparing food, suddenly, that becomes visible.

-Exactly.

If we can't see something, we find it quite easy to kind of ignore.

♪♪ One thing that really drives our behavior is a fear of shame or social rejection.

So the factory workers could see their colleagues stamping the hand and then washing their hands and they didn't want to be part of the group who kind of were deemed unsafe and unhygienic.

-And it did work?

-It did work, yeah.

It actually reduced levels of dirty hands by 63%, which was deemed kind of an acceptable level to operate the factory in.

-To me, it's interesting to think about what really motivates us to make changes, particularly in the middle of a crisis.

Part of it is shame, right?

You don't want to appear to be behaving outside of kind of social norms.

We're social animals.

Were influenced by the behavior around us.

But, to me, there's also a really important sense of solidarity.

I just remember walking around in Brooklyn and seeing, you know, 99% of the people on the sidewalk in open air walking around with masks on, and there was a sense of, you know, we're in this together.

-And I think in societies where you saw that level of coming together in solidarity, what you tended to see later on was that people who had broke rules, people who didn't see themselves as part of this collective effort, they tended to become figures of hate.

That's sort of solidarity does have a flip side to it, which is that those who reject it, they tend to become seen as outside the group, outside the society, letting everyone down.

And what's so important in any of these kinds of situations is the message that one's getting from the top, from our leaders, right?

And so when we find ourselves in the middle of this crisis, in a crisis where our own behavior is so important in determining the outcome, what we see our leaders doing and saying and the messages that they give us is extraordinarily important.

-[ Chanting in native language ] ♪♪ ♪♪ -Throughout our lives, we've been asking people to come to the mosque and now actually we were asking people not to come to the mosque.

It was really surreal.

Throughout our lives, we've been asking people to show love and care by embracing each other, by shaking hands with each other.

Yet now we were asking people not to shake hands with each other.

That was phenomenally difficult for people to understand.

♪♪ One of the elderly members of the community said to me, for 35 years, he'd never missed a Friday prayer.

Some of the young people were saying, "We're absolutely fine, and we can keep the distance from each other.

Why do we have to close the doors of the mosque?"

I was really caught in the middle.

I felt that my leadership was being tested.

And so I had to convince them in the language that they could understand.

Eventually, I think people understood that it wasn't just about them.

It was also protecting everyone in our community.

Once the lockdown was lifted, we had to change the way the mosque operates.

Before, we used to do the handshake to please God.

Now we don't do the handshake to please God Almighty.

Now, it's not easy wearing a mask and giving a sermon for half an hour, you know, I have to do so to lead by example that, look, this is -- if I can do it, others can do it, as well.

I think it's not just talking the talk but walking with people.

You have to constantly tell people that, you know, "We will get through this together."

Maybe standing here socially distant, but God is not socially distant.

Who hears the whispers of the heart.

And that is extremely challenging and emotionally draining as a faith leader, to go through that.

But every day, I have to get up and see that it'll be a better day, and I have to keep on inspiring people.

♪♪ -The COVID-19 pandemic has been the ultimate challenge for our leaders, galvanizing and mobilizing people to adapt to new rules and alter their behavior like wearing masks and maintaining social distance, all to fight the virus.

But the truth is, we've been here before, and there are lessons to be learned from past health crises, starting right here in Philadelphia.

September 1918 -- Philadelphia Public Health Chief Wilmer Krusen hears news of a deadly flu sweeping army barracks across the country... ...as soldiers return from the war in Europe.

Young people are dropping like flies.

In one Boston barracks, 100 deaths in a day are reported.

The U.S. surgeon general warns that influenza is a crowd disease.

To save lives, all social gatherings must be avoided.

This leaves Krusen with a harrowing decision to make on behalf of his community, because preparations are already underway for a massive parade right here in downtown Philadelphia to support the Liberty bonds, which is a major effort to fund the war.

Cities are competing to see who can raise the most money, and parades are a big part of this.

And so, under pressure from the political machine, Krusen decides to ignore the warnings about the epidemic, calling it no different from the normal flu.

The war is the priority, and the show must go on.

And it did.

On the afternoon of September 28th, a two-mile-long parade of 200,000 people packed into the streets of Philadelphia.

Nearly 3,000 miles away in the west-coast city of Seattle, the health chief, J.S.

McBride, reads the same news reports with a growing sense of dread.

On October 4th, just days after the Liberty loans parade, he, too, gets word of a flu outbreak at an army barracks outside the city.

But McBride decides to take a dramatically different course of action.

Enlisting the support of the city's mayor, a stunning public announcement is made.

Schools, libraries, dance halls, pool rooms, cinemas, and churches all must be closed immediately.

When one of the city's theater managers objects, the mayor publicly announces, "Some will kick, but we'd rather listen to a live kicker than bury him.

When pastors complain about closing churches, he says, "Religion which won't keep for two weeks isn't worth having."

It quickly becomes clear that it's going to take more than a few days to get this outbreak under control.

By mid-October, a flu squad has been recruited to patrol the streets.

On their first day, 31 men are arrested for spitting in public.

Even worse, some are publicly shamed with their names printed in the newspaper.

By the end of October, this hard-line health chief really ups the ante, introducing a mask order for the flu squad to enforce.

-Now, they're bulky six-ply gauze and not at all pleasant to wear.

It's no wonder that people resisted them.

But the masks become a symbol of the epidemic in Seattle and all around the country.

Borrowing language used to describe draft resisters, people who refuse to wear the masks are known as mask slackers.

With nothing to do, the people of Seattle retreat to their homes.

Historian Nancy Bristow has studied the 1918 flu pandemic.

-So beautiful.

-Yeah, it's great.

It's kind of fitting to be here in this completely empty theater, given that this very theater would've been closed down in 1918.

-That's right.

Seattle had really strict public closures, so this would've been closed down like so many other public spaces in the city.

-There's been a lot of great music here.

Nancy was inspired by her own family's experience of the deadly virus.

-I grew up very fond of my grandfather, who lived until I was 12, and it wasn't until 1995, when I was fully an adult and he was long gone, that I learned that he had lost his parents within four days of each other in what was probably the fourth wave of the influenza pandemic.

And so he was orphaned.

He was 14 years old, and his younger brother, in fact, was sent to an orphanage.

So, I pretty much kept them with me every day, as I was researching the flu.

A photograph of the four members of the Bristow family sat on my desk to remind me that always, I was talking about real people.

♪♪ -What do the numbers really say about the difference in these two cities' response, between Seattle and Philadelphia?

-I can give you one simple statistic that I think makes it very clear.

For the week ending October 26th, the excess death rate per 100,000 in Philadelphia is around 250.

In Seattle, it's about 40.

Roughly six times higher in Philadelphia than in Seattle.

What was really special about Seattle is that they acted very quickly.

They were willing to continue to increase, make more comprehensive the restrictions they put in place, and they sustained them.

They sustained them over a long period of time.

And those three things in combination -- that was the winning formula.

♪♪ -You have such extensive knowledge of the last terrifying pandemic to hit the United States.

As you've observed the 2020 pandemic, what surprised you and what seemed all too predictable in our response?

-I guess what's surprised me is how much it's been like 1918, that here we were with all of this evidence taken from 1918 that shows, for instance, that social distancing and masking and closures works, and yet, there's resistance.

It's been so disappointing to me.

People are anxious to do the right thing if they have leadership that is clear and direct, that makes very obvious for them not only what's at stake but what they can, in fact, do.

-For all our advances, we're still in the same place.

♪♪ -We've had over 100 years to look for patterns and try to understand why some cities and some countries did better than others in controlling or limiting the spread of the Spanish flu.

We're now in the midst of trying, in real time, as it happens, to understand the patterns that we're seeing with COVID-19.

And if you take the countries that have done well, they don't appear to have very much in common.

Vietnam and South Korea.

Then there's also Australia and New Zealand.

There's Denmark and Ghana.

It's hard to see what links them all together.

This is a disparate picture, and the answer is, we just don't know yet, but it's bound to come down, to a certain extent, to good leadership.

-Absolutely.

Absolutely.

I think, as you say, it's just too early to tell.

But if you look at the history of big changes in public health and the changes in public behavior that have expanded our life-span, sometimes those changes don't come from leadership.

And sometimes the most powerful ones, the most transformative ones come from below.

[ Indistinct chanting ] -In 1980s New York City, in the midst of the AIDS crisis, those changes came from within the gay community.

-Richard.

-Hi.

-It's so good to see you.

-Same here.

-40 years ago, this was the epicenter.

-Yes, it was, because so many gay men who came out in the '70s moved to this area to be close to the center of gay life on Christopher Street.

♪♪ It was the gay promised land.

I grew up in a suburban town, and the one thing people couldn't embrace was homosexuality.

Growing up in that environment and then coming to New York City to suddenly see gay men kissing on the street and no one having to hide, it was life changing.

I was living life in the fast lane.

I went to the backroom bars.

I went to the clubs, the discos.

I went everywhere.

And so I was aware of the whole range of sexual expression and sexual opportunities and what was becoming, like, a bustling sexual amusement park in downtown Manhattan.

-In 1982, as news spread of an incurable disease affecting drug users and gay men, Richard noticed a lump on his neck.

-My doctor at the time, he did blood work, and he said to me, I want you to go for a lymph node biopsy 'cause you have swollen glands.

And I remember thinking, "A gland cut out of my neck?"

-In a New York hospital, a lonely man lies dying of AIDS, but he's not really alone.

15,000 Americans have already died from the disease, and the numbers are doubling each year.

Most people, the first thing they think about is death when you say AIDS.

-If I knew...

I wouldn't be here.

-That's one of the harder parts to deal with.

-Richard was diagnosed with AIDS.

But with the government unresponsive to the suffering, he had to reach out to the community for help.

-So, I met Michael in the first public support group in New York City for gay men with AIDS, and we hit it off right away.

Michael and I said that we needed to reexamine our lifestyle because whatever was spreading, you are more likely to get it the more partners you had.

You couldn't always wait for the government to provide the answer.

You couldn't really trust the medical establishment.

They were often very conservative, and it was really difficult for them to speak publicly about trying to help gay men and other disenfranchised groups who were affected by the epidemic.

We had to figure out how we in our own community could find ways to protect each other.

♪♪ -Richard and his friend Michael, with the help of a pioneering AIDS doctor, came up with their own solution for how to stop the spread of the disease ♪♪ -"How To Have Sex In An Epidemic."

-It was a pamphlet.

This is a historic document.

-Yeah.

What me and Michael wanted to do was to say, we want to empower you by explaining to you how a virus gets transmitted during sex.

That something as simple as a condom could mean that whatever other people are doing, you have it in your hands, the power to protect yourself and your partners.

-There is a way to continue being sexually active.

You just have to make certain changes in the way that you do it, and here, in this booklet... -Right.

-...here is a recipe for that.

-Right.

And we knew when we went to work on this that we were doing something seminal, you know, something that could really curb the tide of the epidemic.

♪♪ -When "How To Have Sex In An Epidemic" first appeared in gay bars and bookshops, some gay men didn't want to listen.

-This was an affront to their belief that the pinnacle of gay liberation was having sex with as many partners as you could as often as you wanted.

♪♪ -But soon, people started to take notice.

-Though we didn't realize it at the time, to ordinary, everyday sexually active gay men and eventually women and people in general, safe sex just struck them as a sensible, rational response to a health crisis that was deadly.

It just made sense.

♪♪ -It took years of activism like Richard's and then the death of Hollywood actor Rock Hudson for the U.S. government to finally wake up to the crisis.

In 1987, six years after AIDS was first detected in the U.S., a commission finally began to investigate and raise awareness of the virus.

-Every morning I get up, I look in the mirror and say, "Thank God you're still here.

-[ Chuckles ] -I mean, the most painful, heartbreaking thing that I ever witnessed in my entire life was watching the friends, the circle of friends that I nurtured and cultivate to be my substitute gay family, you know, was watching one by one, them waking up and realizing that they wouldn't live to see 40.

So when I talk about being old to people, they're like, "Oh, no.

No, you're not old."

I'm like, "Yes, I am.

And I'm proud of it."

-That's the thing that really strikes me about all these interventions.

The sum total of it is the freedom to grow old, right?

That's what it's all about.

♪♪ Richard, to me, embodies a kind of figure that doesn't show up that often in the history of human health, right?

He's not a doctor.

He's not a public health authority.

And yet, he and handful of collaborators are able to come up with this idea and get it into circulation in a way that no one else wants.

And those figures are crucial to the story of our expanded life-span.

-The awful coincidence is the other group who were affected most severely in those early days were people who were taking illegal drugs intravenously, using needles.

It allowed people who wanted to see these two marginalized groups who had been deemed to have transgressed society's norms of, in some ways, being deserving of that, and people like Richard came about and had to take up positions that they took up and take the stance that they took because, you know, our societies, for a few years back there, abandoned part of our community.

-They really had the key because they understood the language of that community because they were members of it.

And getting people to improve their health by changing their behavior, that kind of insider knowledge is often critical.

♪♪ -In 2014, international troubleshooter, OB Sisay, turned his attention to a health crisis that was then taking place in his home country, Sierra Leone.

Cases of the deadly Ebola virus were doubling every three weeks, threatening the lives of hundreds of thousands of people across West Africa.

-This was the most difficult area to fight Ebola.

The capital city, which had all the slums.

-So, these these are campaign maps.

-Yes.

-The language we use when it comes to epidemics is very military.

-Why, it was a war.

We're fighting for the existence and survival of our country.

The world had locked us down.

There were travel bans.

We weren't getting shipping.

We weren't getting imports.

Our people were dying like flies.

Oh, yes, this was a war.

It's just that the enemy cannot be seen and doesn't carry a gun.

-With no effective treatment or vaccine for Ebola, people had to quickly adopt new ways of protecting themselves.

OB started by putting the people of Sierra Leone in charge.

-The problem was that the response at the time was not owned by civil unions.

We were being led by our international partners.

We were not going to be able to be everywhere to stop people infecting each other.

What we had to do was convince them not to infect each other.

And to do that, we had to decentralize power and hand it to the people.

And we had to use their own local leaders, their own languages, their own structures that they trusted.

-And those targeted interventions involves asking people to change their patterns of life.

How did you deliver those ideas to the people of Sierra Leone?

-The message, the messenger, and the medium through which you're communicating is extremely important if you're going to change people's behavior.

One of the first things the government had done was to ban traditional healers from practicing.

But the problem is, these people are an embedded part of our society.

So the practice of just banning them wasn't really working, perhaps rather than consider the traditional healers as part of the problem, why didn't we consider them as part of the solution?

So we reached out to them.

We gave them motorbikes to go and do surveillance for us.

So they became an early warning system for us.

If somebody goes to a traditional healer with a broken leg, they can use their herbs and fix them.

But if they see this person have symptoms of Ebola, they call us.

♪♪ -And there's a tradition in Sierra Leone of relatives washing their dead.

How do you persuade people to change their habits when it comes to something that acutely personal?

-The corpse of an Ebola victim has the highest load of the virus.

It is the most dangerous that you can imagine.

So how are we going to do this to make it both safe and dignified?

Because if you don't do that, people will bury in secret, and you will never contain the virus.

♪♪ So we trained the locals in the burial safety procedures and gave them PPEs.

Training the locals to bury and respect their cultural practices was one of the most significant steps we did to stop Ebola spread.

-[ Speaking native language ] -Armies of young Sierra Leonean volunteers worked day and night until the battle was won.

♪♪ -No more Ebola!

No more disease!

-On the 7th of November, 2015, exactly a year to the day when I had received the call to join the response on the 7th of November, in 2014, exactly one year later, we were declared Ebola free by the World Health Organization, and our city went into jubilation.

And we, for people like me, I couldn't speak.

All I could do was cry.

[ Bells ringing ] ♪♪ -Ebola was defeated by Africans in Africa.

Has the rest of the world been knocking at your door ever since, asking for help on on on how to plan for future epidemics.

-No, they haven't.

They haven't.

So when COVID started, some of us with experience from West Africa have been shouting, saying, we have seen this movie before.

It's not gonna end well for you.

But we have largely been ignored.

If the world had learned its lessons from Ebola, we would have managed COVID very, very well.

But to learn those lessons, the West would have needed to listen to Africans.

-Well, if you have to sit and get told by an African, you're not very used to that.

♪♪ -I was in Sierra Leone a year after the end of the Ebola epidemic, and it felt like being in a country that had been through a war in which they'd been victorious, and there was a strong sense of pride that Sierra Leone had done this.

It's not that the virus had gone away.

It had been defeated by the people of that country, and they had done it.

We mustn't forget, not with a vaccine.

They'd done it themselves through behavioral change.

That's all they had.

[ Indistinct singing ] ♪♪ -And we underestimate that power.

We underestimate the way that behavior change can be harnessed to fight off lethal threats, and I think one of the reasons we underestimate is that we don't spend enough time celebrating the track record of the last 100 or 200 years, doubling the human life expectancy in just over a century.

It's a lot easier to build a war memorial or have a national tribute in memory of some kind of terrible tragedy when we're commemorating lives that were lost, but we don't do the same with lives that were saved.

And I think that's why we have, in a sense, kind of a skewed perspective on our history and don't realize the achievement that all of us have participated in.

-I think we've imagined and we've assured ourselves that this new world that we live in is permanent, and the idea that we can slip back into the world our ancestors knew is almost too horrific to contemplate.

-Yeah, I think there's this belief that there is this inevitable ladder of progress.

Once you start curing diseases and extending life the way we've done over the last century or so, that that march of progress will just continue.

But it doesn't.

♪♪ New threats emerge, and so we have to continue the work, inventing new solutions, figuring out new ways to collaborate and sharing those to fight the diseases of the 21st century.

♪♪ -Okay.

So Steven can't see me anymore.

-I can hear you, though.

-Okay.

No, no.

It's fine.

Steven, I will one day get on an aeroplane.

I will one day be in the United States.

We will one day have lunch.

-[ Laughs ] -[ Laughs ] -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.

-He modified the process and arrived at vaccination.

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

-Immune system bootcamp.

[ Laughs ] -How can you make a vaccine if you don't have the pathogen?

Well, all you need is a computer screen.

-This is arguably the biggest story in human history, how we doubled our life expectancy.

♪♪ ♪♪ ♪♪