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  • Thanks to Brilliant for supporting this episode of SciShow.

  • Check out Brilliant.orgSciShow to learn more.

  • [♪ INTRO]

  • Two of the vaccines we have for COVID-19 have the distinction

  • of being the first mRNA vaccines to see widespread use in humans.

  • It's a vaccine technology that uses a type of molecule called RNA

  • to teach our cells how to resist disease.

  • So how do they work, and how are they different

  • from the litany of immunizations you probably got as a kid?

  • Let's take a look. All vaccines do one basic thing.

  • They imitate a disease-causing agent, or pathogen,

  • with the goal of ratting it out to your immune system.

  • Then, your immune system knows what to do if that pathogen ever shows up.

  • mRNA vaccines do that too, but they represent a departure

  • from the way we've introduced pathogens in the past.

  • Most of the time, we've used a bit of the real thing.

  • Like killed pathogens, or living ones that have been weakened.

  • Or just pieces of them, or even substances that bacteria just make.

  • In any case, these bits our immune system can spot are called antigens.

  • Each antigen has a shape unique to a particular pathogen.

  • When you get a vaccine,

  • your immune system sees the antigen and sounds the alarm.

  • That triggers the formation of memory cells that remember the bad guys,

  • as well as antibodies that disable the pathogen if it tries to invade in the future.

  • Now, mRNA vaccines still accomplish that goal.

  • But instead of pieces of pathogens, or any other strategy we've used in the past,

  • they contain messenger RNA, or mRNA for short.

  • It works sort of like giving our cells a build-your-own-antigen kit

  • instead of the actual antigen.

  • The end product is the same, but we've asked our cells to do the heavy lifting.

  • That's because cells are kind of better at this stuff than we are.

  • We can mess around with pathogens all day,

  • but cells already know how to make antigens if we just supply the instructions.

  • It's not the only way to design a vaccine fast,

  • but it's a great tool to have handy when a pandemic comes along.

  • So how do you program a cell to make an antigen?

  • Well, the simple version is, you just borrow the machinery it's already using.

  • See, most every cell contains a complete copy of our genome,

  • the sum total of instructions it takes to make us, written in DNA.

  • That information gets translated into proteins,

  • which do all the actual work of being alive.

  • Every protein has a job, specified in the DNA instruction manual.

  • When it's time to make a protein, the cell needs to reference those instructions.

  • But DNA remains in one spot: the nucleus of the cell.

  • Proteins, meanwhile, are made outside the nucleus.

  • The solution is to copy out the instructions

  • and send a message outside the nucleus.

  • You might see where this is going.

  • That message is made of messenger RNA,

  • which contains a copy of the DNA instructions for use in protein-making.

  • The message exits the nucleus, and makes its way to a ribosome in the cell.

  • This piece of machinery reads the mRNA and translates the message into a protein.

  • This is where the clever part comes in, because we know the genetic code

  • so we can write our own message for the cell to translate.

  • That's what an mRNA vaccine is: a coded genetic message from us to our cells,

  • for them to work out with their molecular decoder rings.

  • Instead of an antigen, they contain the mRNA template to build an antigen.

  • In the case of our COVID-19 vaccines,

  • the message codes for an antigen called the spike protein.

  • These spikes stick out of the virus,

  • which uses them like a key to unlock and infect people's cells.

  • When the shots go into people's upper arms,

  • the mRNA molecules inside make their way into cells and to ribosomes,

  • which are more than happy to do their job and translate the message.

  • Our cells display the finished spikes on their surface.

  • Our immune system spots them and starts taking action.

  • From there, it's thought that things work pretty much the same as more traditional vaccines.

  • The immune system makes memory cells and antibodies,

  • and once those defenses have kicked all the way in, boom.

  • You're ready to fight off the real deal.

  • But while we hope those memory cells will last a while, the message doesn't.

  • It never finds its way into the nucleus, so it can't mess with our DNA master blueprint.

  • Which means it's not manipulating our genes or anything

  • The effects really are a lot like every other vaccine you've ever gotten.

  • These mRNA vaccines were designed pretty quickly in response to the pandemic,

  • but that doesn't mean they came out of the blue.

  • In fact, scientists have known about the potential of mRNA vaccines for decades.

  • But it's taken years of testing and tweaking to get the technology right.

  • For example, researchers had to figure out how to make the RNA molecules

  • last long enough in our bodies to actually get translated.

  • And they had to work out the perfect delivery vehicle

  • to get the mRNA into cells, and minimize side effects.

  • Even with all that in hand, before now,

  • no RNA-based vaccine had ever made it out of clinical trials,

  • and there was no guarantee they'd ever work.

  • But the ones we have for COVID-19 do work.

  • At least, to the best of our knowledge so far,

  • they're safe and effective enough to help get the pandemic under control.

  • And with the technology showing such promise, there's renewed interest

  • in some older mRNA vaccine efforts for things like rabies and Zika.

  • Some could even fight cancer.

  • So that's what an mRNA vaccine is:

  • a novel form of vaccine that teaches your cells

  • how to make something your immune system can learn from.

  • They're not as different as you might think, but they have a ton of potential.

  • mRNA vaccines are an elegant way to address a global crisis.

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  • Like their course on complex numbers,

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  • considered one of the most beautiful equations in all of math.

  • Brilliant has tons of courses in math, science, engineering, and computer science,

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  • If you're interested, you can check out brilliant.org.scishow

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  • And by checking them out, you're also supporting us, so thanks.

  • [♪ OUTRO]

Thanks to Brilliant for supporting this episode of SciShow.

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