Story at a glance
- Coronaviruses mutate at a slower rate compared to influenza viruses.
- Many experts think there is currently only one strain of SARS-CoV-2.
- A mutation in the genetic sequence does not necessarily lead to a new strain.
The coronavirus has been circulating amongst humans around the world since at least late fall of 2019. Half a year later and many nations in the world are struggling with COVID-19 cases.
Researchers are studying how the coronavirus is changing and whether there might be different strains of the virus. What could that mean for us?
What do mutations do
A mutation potentially does nothing. Any variations that lead to a meaningful change to the genetic code would need to change the way the genes function. This is harder than it may seem.
Changing one nucleotide in a genetic sequence, called a point mutation, may not change the function of the gene. It takes three nucleotides to code for one amino acid when translating the genetic sequence into a protein. Some three nucleotide codes are redundant and code for the same amino acid, so changing one of the nucleotides may not change the amino acid it codes for. It’s a little more complex than that, but that is the basic idea.
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Many viruses that jump from animals to humans have done most of the necessary genetic changes by the time it is infectious and spreading. The virus most likely needs to get passed between a wild animal like a bat and a domestic animal. Influenza is known to pass between birds, pigs and humans. Pigs in this case are the “mixing vessel” where the virus can adapt to mammals. After the jump from a wild animal to an intermediary animal, the coronavirus may have been passed between humans and domestic animals several times before it becomes able to spread by human-to-human contact. This was the concern with bird flu, that it would become better able to spread among humans. But that didn’t happen, and most cases of bird flu were passed from a bird to a human.
Rate of mutation
Some families of viruses are known for quick mutation rates. For example, influenza viruses have a fast rate of mutation. Coronaviruses don’t mutate as quickly as flu viruses, but they do mutate.
What does this mean for us? It means that it could take a long time before any additional changes to the genetic material of SARS-CoV-2 before we see anything truly change in how it affects us. Even if there are mutations, that may not translate into a different manifestation of the disease it causes in people.
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One strain or many strains?
Many virologists currently believe there is still only one strain of SARS-CoV-2, even though there have been reports of multiple strains. There are differences in the genetic sequences, but that does not necessarily add up to separate strains. Sure you can map out differences between a virus sequence from New York and a virus sequence from Washington. But just because there are slight differences in the genetic material does not mean a whole separate strain has emerged.
Experts are still trying to understand what the virus does in our bodies, and they are discovering new symptoms even now. But to qualify as a separate strain of SARS-CoV-2, there may need to be significant differences in how the viruses behave in our bodies or how they are transmitted.
Ed Yong of The Atlantic compares this to dog breeds. All dogs are the same species, but there are many breeds. Some differences within the breed, like coat color, do not warrant putting individual dogs into separate breeds. A dog breed is like a strain of viruses.
Currently, most experts think that we don’t have any evidence that there is more than one strain, although new evidence could come up in the future. In this case, SARS-CoV-2 is its own species of coronavirus, of which there is currently one strain that is circulating in humans.
For up-to-date information about COVID-19, check the websites of the Centers for Disease Control and Prevention and the World Health Organization. For updated global case counts, check this page maintained by Johns Hopkins University.
You can follow Chia-Yi Hou on Twitter.
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