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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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