Thread by @mentalplex

An RNA vaccine explainer, with background:

Part 1: How do your cells make things?

Each cell in your body with a nucleus contains all the plans needed to make another you, as DNA. These plans are stored in the nucleus (an envelope inside the cell). They need to stay just as they are, for generations, and need to be copied without error when your cells divide.

In any given cell, most of those DNA plans are rolled up and put away. A brain cell doesn't need to make digestive enzymes, so it rolls up those plans and hides them away. A complex set of signals controls how a cell decides what to make and when.

When it is time to make something, a part of the DNA plan is unrolled and transcribed into a message (mRNA). The message is sent out of the nucleus into the rest of the cell, containing information about what to make, how to make it, how much to make, and where to put it.

When the job is done, mRNA isn't stored anywhere. It's shredded and recycled for parts. Unlike DNA, mRNA isn't replicated, and doesn't have to sit there for generations without changing. It's a short lived set of specific instructions about what to make at a very specific time

So that's part 1, how your cells make things. Remember, mRNA is a message, a short lived set of specific instructions about what to make at a very specific time. Lets move on to Part 2: the immune system and vaccines...

In order for your immune system to fight off an infection, it needs to know how to recognize the infectious agent. Let's call those infectious agents "foreign agents" (sorry @Garrett_Archer).

Your immune system is very powerful. It has many different ways to get rid of foreign agents. It can shoot them full of holes, throw them to hungry monsters, drown them in acid, and more. All it needs to do is learn how to recognize them.

Some foreign agents aren't very clever. They have obvious bad intentions, and pretty much any foot soldier can spot them. These foreign agents don't get very far. Others are more clever and it takes a while to find them.

Once the immune system finds a foreign agent, though, it will recognize it again almost right away.

Vaccines work by giving your immune system a head start. Some basically drop a dead agent in front of the surveillance team. Others use key parts of foreign agents, proteins that they need in order to infiltrate your body. The Moderna and Pfizer vaccines use messenger RNA (mRNA).

Remember mRNA from above? The specific short lived set of instructions about what a cell should make? When the vaccine is injected into your arm, these messages are gathered up by cells from your immune system that collect little things that have been lying around.

These collector cells follow the instructions in the vaccine message, make a protein, and show that protein to other cells in your immune system that coordinate your immune response. When they've made enough of the protein, the message is shredded and recycled for parts.

From here, the process works as for any other vaccine. The protein those collector cells made is a SARS-CoV-2 protein, a protein that happens to be necessary for you to develop COVID-19. So it will now recognize that foreign agent if it shows up, almost right away.

Unlike natural immunity, your body didn't have to expose itself to an infection in order to learn how to recognize this foreign agent. All you needed was a message from the vaccine ("make this much of this protein, put it here") and now your immune system knows what to look for.