How Mutation Leads to New SARS-2 Variants

This is a brief post on the issue of new COVID variants and their cause. There has been a lot of confusion as how new variants arise. For small biological organisms that evolve quickly (bacteria, viruses, parasites, some insects), new strains can arise relatively quickly. I say relatively because it can still take many years in some cases. This is because small changes in genetic material can lead to important changes in function.

Point Mutation: There are 3 kinds of mutations that can cause this. One is a point mutation, a change in a single nucleotide (the basic unit of genetics, like a letter of the alphabet). Depending on the point mutation, this can lead to no change at all, or an important change that can have an impact on drug resistance, protein binding to target, or other effect. This is particularly likely in viruses whose genome are made from RNA, because the proteins that make RNA strands in these viruses are particularly error prone. This is why HIV, the Flu, and Coronaviruses can change so quickly.

Genetic Re-assortment: Another kind of change common in some viruses like the flu, is a re-assortment of chromosomes, or “antigenic shift”. The Flu virus genome comes in 8 pieces. If 2 viruses infect the same animal and the same cell, then that cell can produce new viruses that have a combination of pieces from both infecting viruses. This often happens when a pig on a farm somewhere gets infected with 2 flu viruses, and produces a new, novel form of the flu. This is why new flus are often called a “Swine Flu”.

From the Wikipedia page on Influenza.

Conjugation: Bacteria can donate genetic material to other bacteria, even those of a different species, in a process called conjugation. Yes, it’s more like that than you might imagine. In this fashion, bacteria may acquire large amounts of new DNA. These new DNA fragments are kind of like software downloads, encoding whole new abilities like drug resistance, iron scavenging, and the ability to bind and invade new cell types. In fact, it could be argued that many or even all disease causing bacteria are this way because they’ve inherited DNA from other bacteria!

So how does this all relate to SARS-2? COVID changes using the point mutation route, which it does quickly because it has an RNA genome. The probability of a new variant arising is dependent on the speed of mutation, the number of viruses that exist, and time. This means that the more viruses that exist at any moment, the more likely that a new strain will arise. In our present moment, this means that the more people in the world that have COVID, the more likely a new variant will arise. This is a concern at a time when new infections are high.

The very good news is that the vaccines we have appear to work on all the existing variants, at least to some degree. So while we do need to try to keep the number of infected people down to avoid new variants, we are not defenseless against them. But there is a possibility that a new variant will arise that is not neutralized by the current vaccines, and this should be avoided of course.

Don’t fear, but be smart!

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