Most readers probably know a little about how vaccines work. By exposing our immune system to weakened germs, or even fragments of germs, we can trigger the body’s natural immune response. This response prepares the body to fight the germs later when we eventually encounter them at their full strength. A good vaccine gives you disease resistance as if you’ve been sick, but without the costs of getting sick.
That’s how the COVID-19 vaccines work, too. The details vary, but all the available COVID vaccines teach a few of your cells to produce coronavirus spike proteins, the little knobs on the outside of the virus that you see in all the pictures. The spike proteins can’t give you COVID, but their presence is enough to teach your immune system how to fight the coronavirus.
How do the vaccines teach your cells to make the spike proteins? Well, it depends which one you get.
The Moderna and Pfizer vaccines are mRNA vaccines. To understand how these vaccines work, you need to know a little about how your cells work. Your cells are constantly manufacturing proteins. Normally, the nucleus, the part of the cell that contains genetic information, writes the instructions (mRNA) for building a protein. These instructions are then passed off to the ribosome, the cell’s protein factory, which builds the proteins.
The mRNA vaccines bypass the nucleus, handing a set of instructions directly to the ribosomes in some of your cells. These cells will produce coronavirus spike proteins. The instructions in the vaccine break down after a short while and your cells stop producing the spike proteins, but your body remembers how to fight the virus long after. MRNA vaccines have been in development for about 30 years.
The Johnson & Johnson vaccine takes a different approach. This vaccine uses a mild virus—more specifically, an adenovirus—that has been modified so that it can’t make you sick.
Normally, an adenovirus would enter a cell and use the cells' hardware to make copies of itself. That’s what all viruses normally do: hijack host cells and use them to self-replicate. But the adenovirus used in the vaccine has been altered so that it can't self-replicate. All it can do is enter a cell and make some coronavirus spike proteins. Similar adenovirus vaccines have been around for about 50 years. The ebola vaccine is an adenovirus vaccine.
So that's how the COVID-19 vaccines work. They recruit a few of our own cells to make spike proteins, and then our immune systems use those proteins to gear up for the coronavirus. Pretty ingenious, right?