[MUSIC] Orange you glad you don’t have scurvy?

In 1747, in the first medical trial ever performed, Scottish physician James Lind found out that eating citrus fruits could cure scurvy.

Today we know this works because citrus contains high levels of vitamin C, in fact ascorbic acid, a common name for vitamin C, comes from the Latin for not scurvy.

By issuing rations of lemon juice to sailors, the British Navy was able to pretty much eliminate the disease… until the late 1800’s when polar explorers suddenly began to see scurvy again… the copper pots holding their lime juice had destroyed the vitamin C. But they were pretty confused.

So despite James Lind’s experiments 150 years before, citrus fruits became the enemy, and when Robert Falcon Scott set out to reach the South Pole in 1911, he carried the finest in canned meat products, biscuits, chocolate, tea… and zero vitamin C. A Norwegian team beat them to the Pole by five weeks, and during their sad journey home, Scott and his team perished in a blizzard, sick and weak from what was probably scurvy.

It had been so long since anyone had seen this disease, the British had forgotten how to prevent it.

When we create such effective solutions, we can forget how serious the problems were.

Thankfully, people today don’t die of scurvy.

Or polio.

Since the introduction of Jonas Salk’s polio vaccine in 1955, the disease has been nearly eradicated from Earth.

"The thing to remember is that this is a continuous process" Compare the 358 infections reported in 2014 to the 1940s, when half a million people per year were paralyzed or died from polio infections.

Vaccines… work.

Our immune system is on constant alert against germy baddies, with millions of white blood cells each on the lookout for specific infections.

When an immune cell meets its target, it replicates itself and this clone army sends a barrage of protein weapons called antibodies to label the trash for cleanup.

After the infection is gone, so-called memory cells stick around, ready to mount a fast attack in case the germ shows up again.

This is how we develop immunity, and it works pretty well… since we’re all still alive.

But even with all that, some super-bad germs can take us out before our immune sentries have had time to call up that clone army, this is especially true for young children, their immune systems are fresh out of basic training.

Thankfully we have vaccines, which are made of tiny pieces or weakened versions of viruses or bacteria.

They let our immune system see what the bad guys look like, and recruit those all-important memory cells before we ever have to actually see the real enemy.

Thanks to vaccines, the U.S. was able to eliminate measles in the year 2000… But, in recent years, as more and more parents are refusing to vaccinate their children, or are vaccinating them later than what doctors recommend, it’s back.

In most states, more than 90% of children are vaccinated, but that’s not enough to keep a disease like measles at bay.

In our episode about Ebola, we talked about a number called R0, the basic reproduction number for a disease, or the number of people infected by one person in a susceptible population.

For Ebola, that number is low, but for measles each sick person will infect up to 18 others.

Luckily, vaccines can change that.

The fraction of people who are vaccinated, or immune, can lower the reproduction number below 1, which means the disease is disappearing.

90% of unprotected people who come in contact with somebody who has measles, even just breathing the same air, will become infected.

To control a super-contagious virus like that, the vaccination rate has to be 95% or above, now right now the U.S. is lagging behind, and measles is making a comeback.

The Guardian put together a simulation of just how this so-called herd immunity works.

When enough of a population is vaccinated, even if it’s not 100%, the herd can protect the unprotected.

With vaccine refusal on the rise, our herd immunity is breaking down.

Preventable diseases like measles and whooping cough have become our scurvy.

Most of us don’t know anyone with polio.

And I mean… measles, it’s not that bad, right?

Well, yes.

It is that bad.

Before the age of vaccines, millions of people were killed by diseases that today are just bad memories.

Vaccines have let us develop a sort of generational amnesia, today we expect our children to grow up healthy, and we’re lucky that we don’t appreciate just how dangerous these diseases are.

Like science writer Seth Mnookin says, “vaccines are victims of their own success”.

Because of stories like Andrew Wakefield’s discredited study wrongly linking vaccines and autism, and the news media’s obsession with using pictures of crying, terrified children being poked with needles, people are nervous about vaccines.

This anxiety isn’t new, though.

When Edward Jenner, in 1798, saw that milkmaids didn’t catch smallpox, he realized that because they had been exposed to the similar cowpox disease, they were immune, and based on this, he developed an early smallpox vaccine by inoculating humans with the cow virus.

In fact, the word vaccine itself has bovine origins.

Still, as far back as 1802, critics were claiming that the smallpox inoculation would turn you into a cow.

Vaccines don’t come without risk.

Nothing does.

But on average fewer than one in a million people will experience a dangerous reaction to common vaccines.

Car accidents, playing outside, even walking will injure more children.

Vaccines aren’t like other medicines: you get sick, you take something, you get better.

They’re something we take when we’re well, to stay well.

They’re using disease to prevent disease, an invisible shield preventing an invisible attack.

Vaccines are asking us to do something altruistic, to make a choice to protect not only ourselves and our children, but also those around us.

Author Eula Biss says that vaccines are one of the most empathetic things we can do, "a system that’s based on people voluntarily using their bodies to protect other vulnerable people".

That’s something I hope we don’t forget.

[OUTRO] Now, I’m a doctor, but I’m not that kind of doctor.

It’s natural to have questions about vaccines, and you should have a conversation with your medical professional.

They want the best for you and yours.

I will give you one prescription, though, and that’s to subscribe, so you can get a full dose of science, every week.

If you want to read some amazing books about vaccines, check out Seth Mnookin’s “The Panic Virus”, and “On Immunity” by Eula Biss, links in the description.

Stay curious.