You can learn more at Brilliant.org/SciShow.

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Okay, so hopefully it's not too shocking to hear that the measles vaccine saves lives.

Before widespread measles vaccinations were a thing, the measles virus caused over four

million deaths a year.

Thankfully, since measles vaccines started making their rounds more than fifty years

ago, there's been a decline in childhood mortality.

A massive decline, in fact.

Deaths of children have dropped by up to ninety percent in lower income countries.

And that's…a lot more than you'd expect if the measles vaccine just prevented deaths

from the disease itself.

Turns out vaccinated kids are also not dying from other illnesses that occur as secondary

infections or within a few years.

And that's because measles messes with your immune system in a unique way, leaving you

susceptible to illnesses you were previously immune to.

Yeah, the measles virus is /that/ nasty.

Your immune system works really hard to keep you protected from illnesses.

And one way it does that is with your adaptive immune system—basically, a whole army of

cells that can learn from pathogens.

Among the most important weapons in the adaptive

immune system are lymphocytes, special white blood cells that can remember what's tried

to take you down before, so next time it comes around, your body is ready.

T cells are a type of lymphocyte, for example, and they have the essential task of finding

unhealthy or infected cells and destroying them.

There are also B cells, which bind to intruders, and alongside T cells, help create antibodies

during an infection.

And while they're fighting what ails you, B and T cells also create memory cells.

These are clones of the specific B and T cells which successfully bound to the pathogen.

And they remain after an infection holding onto information about each threat the body

has been exposed to.

Basically, they create an immune system memory bank of the bad guys you've battled off.

We know from studies in both macaque monkeys and humans that the measles virus attacks

and kills B and T lymphocytes.

So it might literally wipe out part or all of your immune system's memory bank.

And although white blood cell counts in your blood return to normal levels after a few

weeks, it's likely these replacement B and T lymphocytes are measles-specific.

So your immune system might successfully beat the measles virus and create a life-long immunity

to it, but it could also stop remembering a lot of what it knew beforehand.

Initially, it was thought that this immune amnesia effect only lasted for the weeks immediately

following infection.

And that might make sense if the virus doesn't wipe out your entire clone army.

But a growing body of research suggests it lasts way longer than that.

Data on childhood health that's been collected worldwide since measles vaccines first became

widespread suggest the virus disables immune memory for two to three years.

In one study, researchers looked at the medical history of over two thousand measles patients

compared to children who never caught the measles.

Their work showed that children who once had measles were diagnosed with more infections

and were given more anti-infection prescriptions than the measles-free population for up to

five years after recovering from the measles.

To put it not-so-lightly, someone who survives a bout of measles could become infected with

a life-threatening disease years later that they would have otherwise fought off easily.

Scientists are still trying to figure out the exact mechanisms for this.

Some studies suggest the live measles vaccine itself helps by directly enhancing your immune response.

You see, in addition to B and T cells that take on intruders and remember past wrongs,

there are other immune cells which use nonspecific defenses against foreign cells in the body

The measles vaccine might make these innate immune cells more responsive when they reencounter

familiar pathogens in a way that's totally unrelated to antibodies—something referred

to as trained immunity.

But other research suggests that measles vaccines simply prevent the immune amnesia effect from

happening.

You know, by stopping the measles infection in the first place, and therefore, preventing

it from killing off your memory cells.

There are other questions about all this, too—like, how much immune memory is erased

by the virus.

For example, if you get the measles after other childhood vaccines, does it essentially

wipe them out?

Right now, we just don't know, though there are doctors trying to develop tests that can

figure out what protections you've lost.

Because of these and other unanswered questions about measles infections, the best bet is

to protect everyone from getting measles to begin with!

Seriously, get vaccinated.

When enough people get vaccinated for infectious diseases like measles, it protects everyone,

not just those who get the shot.

Herd immunity ensures there isn't a large enough susceptible population to continue

the spread.

And that protects people who can't be vaccinated and other vulnerable individuals, like babies

or people with compromised immune systems.

But if you really need another reason to get the measles vaccine, here it is: you're

not just protecting yourself and others around you from the measles.

You're also helping to keep your immune system in good working order, so it can protect

you from all sorts of other illnesses.

Because no one wants a forgetful immune system!

No one wants a forgetful, well, anything, really.

Forgetting is no fun.

So if you want to be sure you remember all that science and math you learned in high

school and college, you might want to check out Brilliant.org.

You see, Brilliant offers interactive courses in math, science, engineering, and computer

science.

So whether you're looking to brush up on subjects you took years ago or learn something

new, they've got you covered.

And you can try their Daily Challenges, too.

There's a new question every day, so you can apply all the information you've learned

or re-learned from their courses.

Also, they're totally free.

And if that's not cool enough, the first two hundred people to sign up at Brilliant.org/SciShow

will get twenty percent off an annual Premium subscription.

So you can challenge your brain all year long and support SciShow in the process.

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