Tl;dr: mutations can make vaccines less effective, but that doesn’t mean they render them useless. Immunity isn’t all or nothing, and the current vaccines still provide protection, especially against severe disease and death.
Many have been concerned that because (so far) our COVID vaccines have used the spike protein from the original SARS-CoV-2 virus (also called the OG), any mutations in the spike protein will make the vaccines ineffective. Luckily, this isn’t how it works.
The spike protein is 1273 amino acids long. When our immune systems respond to the spike protein from the vaccines, we make antibodies that cover all over its surface. Imagine a fluffy cat rolling around in a field of sticky burrs — the burrs are going to get all over the cat’s fur. In the same way, the antibodies stick all over the spike protein.
But unlike burrs, antibodies are unique. Each individual antibody only clings to one specific part of the spike protein surface, latching on based on the shape of the surface at that particular spot. Collectively, all of these unique, individual antibodies coat the spike protein.
This means that if you are vaccinated for COVID, you don’t only have one type of antibody that binds to the spike protein, you have many different types of antibodies that bind different parts of the spike protein.
Now, to variants. A single mutation usually alters only a single amino acid, which generally only slightly changes the shape of spike protein. It’s like altering the shape of one lego in a lego master piece.
If there was an antibody that bound exactly where that amino acid change occurred, then maybe that one particular antibody won’t work as well any more. But because we have many different unique antibodies that target different parts of the spike protein, the spike protein will still be covered with antibodies in other places on the surface. So one single mutation generally doesn’t pose too much of a threat, because it won’t change the shape of the spike protein too much, and the majority of our antibodies will still work very well.
The trouble occurs when there are enough mutations to change the shape of the spike protein significantly. If this occurs, then a higher percentage of our antibodies* won’t stick. This is part of why omicron has infected so many people — there were enough mutations in omicron’s spike protein that it’s shape changed quite a bit, making both immunity from prior infections as well as vaccine-induced immunity less effective. However, less effective doesn’t mean not effective at all: there is still enough similarity to the OG spike protein that the current vaccines do provide some protection, especially against severe disease and death.
*Antibodies are not our only defense against COVID; T cells are another part of the immune system that play an important role in protecting against SARS-CoV-2 infections.
In conclusion, the spike protein lego masterpiece is made up of 1273 different legos, and our immune response creates multiple different antibodies that bind different pieces of that lego masterpiece.
Swapping out a few legos (mutations) is generally not enough to render that antibody arsenal totally useless, but it can make it somewhat less effective.
Stay safe. Stay well.
Those Nerdy Girls
You Can Know Things: Where New Variants Come From
Dear Pandemic: Everyone I know is getting Omicron. Does this mean the vaccines don’t work? (from January 2022)