How MRNA Vaccines Work
The first COVID vaccine introduced in the United States from Pfizer and BioNTech is an mRNA vaccine. The second is likely to be, too: the Moderna vaccine is under review this week. We’ve never had a widespread mRNA vaccine before, so you’re not alone if you’re wondering what the hell this technology is and if it has anything to do with DNA.
To answer the most common questions: no, it doesn’t change your DNA. No, this is not an unsubstantiated technology (in fact, it has been in development for decades ). The CDC has a newsletter with the basics you need to know about the new technology.
But here’s a very short version: The mRNA in the vaccine contains instructions that tell our bodies how to make the coronavirus spike protein. As soon as we do this, our immune system loses its temper as expected and produces antibodies to the spike protein. The mRNA is destroyed shortly after injection, but antibodies remain. They can then recognize the real virus if we ever meet it in the wild.
Want a longer, more detailed version? Like this.
Our cells contain DNA and constantly produce mRNA.
Let’s start by recalling what it means to have genetic material. The DNA that we humans have is contained in (almost) every cell in our body. It includes instructions for everything the cell can do. Processing food, growing more cells, releasing hormones – everything that happens in your body happens because your cells follow recipes encoded in your DNA.
Every time our cells use one of these recipes, the information must first be copied into DNA. This copy, instead of being another piece of DNA, is a slightly different type of molecule called RNA. (It’s as if the DNA were a collection of reference books in the library. You can’t check a book because it should stay in the library, but you can write the information you want on a notebook and take it with you. A notebook is RNA.)
Copying DNA to make RNA is a process called transcription , and the next step is often translation : using RNA instructions, now called mRNA, to make a protein. Proteins make up a large part of the structure of our body, and small machines made of proteins perform almost all the functions of our body. We constantly create mRNAs and use those mRNAs to make proteins. All the time.
The “M” in mRNA stands for “messenger,” and it refers to the type of RNA we’re talking about here — those that carry information from DNA to protein-making machinery. (There are many other RNAs out there in the world, but let’s not get too lost on the way.)
Wild coronavirus contains RNA instructions to build itself
Before we talk about a vaccine, let’s take a look at how the virus that causes COVID, SARS-CoV-2, works in the wild. Viruses are smaller and simpler than any of our cells, and many scientists will argue that they are not “alive” like humans or even bacteria.
The virus consists of proteins, sometimes enclosed in a lipid (fatty) membrane. The proteins themselves make up the spiky ball of the coronavirus. The red ridges in that iconic illustration you saw are spiked squirrels, but we’ll talk about them later. The rest of the virus is made up of another 28 proteins .
And inside this spiked ball? This is one long strand of RNA. This RNA is the genome of the virus and contains instructions for making all 29 proteins in the virus itself.
When a virus infects our cells, our own protein making machine translates the viral RNA and makes the proteins it needs. We were deceived; we just did a bunch of viral parts. These pieces are assembled into new viruses, each with its 29 proteins and a fresh copy of their RNA, and then sent out into the world to infect more cells.
(Again, I’m giving you a very simplified overview of what’s going on; this article from Nature describes the life cycle of the coronavirus in all its tedious details.)
mRNA vaccines instruct our cells to make a spike protein
A conventional vaccine must include at least one protein from the virus or bacterium it targets, possibly a whole virus that has been inactivated or attenuated so that it cannot replicate. But the mRNA vaccine works differently.
This vaccine doesn’t give us any proteins at all, just a small lipid bubble (similar to micelles in micellar water, make-up cleanser) containing RNA with instructions on how to make the spike protein. These instructions are even formatted as a beautiful human-type mRNA, rather than a special complex structure of viral RNA.
By following these instructions, our cells can make a spike protein (a set of those red bumps), but that’s about it. The remaining 28 proteins are absent. So we won’t make viruses by accident.
Our immune system can then respond to the spike protein.
Once the spike protein has been created, cells can place the spike proteins outside where the cells of the immune system can interact with them. Our immune system recognizes the spike proteins as foreign, not part of ourselves, and develops an immune response against them.
The immune response may include soreness, fever, or fatigue. But you are not sick; your immune system simply reacts to the protein release and prepares to recognize it in the future.
The mRNA of the vaccine is rapidly disappearing
There is no mRNA vaccine left. Just as our cells always make mRNA, they also destroy them all the time. mRNA is a temporary messenger that is used and removed in a matter of seconds after creation.
Although RNA and DNA are nucleic acids, and both are “genetic material” in a certain sense (DNA is our genetic material, RNA is the genetic material of a virus), mRNA cannot become part of our DNA and does nothing to alter our DNA. It is a different type of molecule found in a different part of the cell.
Why mRNA vaccines?
Several types of vaccines are being tested for COVID. Many use traditional technologies such as modifying the common cold virus so that it cannot replicate, and therefore it also includes the spike protein of the coronavirus.
But mRNA vaccines work especially well in this situation because they can be made so quickly. If you want to make multiple doses of the vaccine, you need to somehow grow these viruses. For example, the flu vaccine is grown in chicken eggs .
MRNA vaccines are faster because you don’t need any cells to make them. The technology for creating mRNA vaccines has been developed for many years, and 2020 was just the time for them to shine. If you’d like to know more about how the vaccine was developed so quickly, we have an explanation of this .