Previous: 5 Mosquito Magnets
Next: These Animals Don’t Need Oxygen?!



View count:99,193
Last sync:2022-12-03 23:45
Since measles vaccines started making their rounds, child mortality has dropped by up to 90% percent in some countries. That’s more than you’d expect if the measles vaccine just prevented deaths from measles. Can science explain this increased survival rate?

Go to to try out Brilliant’s Daily Challenges. The first 200 subscribers get 20% off an annual Premium subscription.

Hosted by: Stefan Chin

SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at
Support SciShow by becoming a patron on Patreon:
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:

Adam Brainard, Greg, Alex Hackman, Sam Lutfi, D.A. Noe, الخليفي سلطان, Piya Shedden, KatieMarie Magnone, Scott Satovsky Jr, Charles Southerland, Patrick D. Ashmore, charles george, Kevin Bealer, Chris Peters
Looking for SciShow elsewhere on the internet?

This episode of SciShow is supported by Brilliant.  You can learn more at

SC:  Alright, 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 4 million deaths a year.  Thankfully, since measles vaccines started making their rounds more than 50 years ago there's been a decline in childhood mortality.  A massive decline.  

Deaths of children have dropped by up to 90% 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.  But it 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!

You're 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.  

For example, T cells are a type of lymphocyte and they have the essential task of finding unhealthy of 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 are fighting what ails you, B and T cells 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 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 your 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 the infection, and this might make sense if the infection 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 2 to 3 years.  

In one study, researchers looked at the medical history of over 2000 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 mealses-free population for up to 5 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.  And scientists are still trying to figure out the exact mechanisms for this.  

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

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, like the ones that are a part of what's called your innate immune system. And 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 the measles vaccine may 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.  

But 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 than 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 people get vaccinated from infectious diseases like measles it protects everyone.  Not just those who got 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 nobody wants a forgetful immune system.  

Well, no one wants a forgetful 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  You see Brilliant offers interactive courses in math, science, engineering, and computer science.  So whether you are 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 are totally free.

And if that's not cool enough, the first 200 people who sign up at will get 20% off of an annual premium subscription.  So you can challenge your brain all year long and support Scishow in the process.