Is there a limit to how much the coronavirus can mutate?

The possibilities are seemingly endless.

The coronavirus is mutating, picking up genetic changes as the world races to vaccinate people as fast as possible.

It’s normal for viruses, including SARS-CoV-2, to mutate. But is there a limit to how much the virus can mutate and still make people sick — or can the virus just continue to evolve indefinitely?

It turns out there is a limit, but we don’t exactly know what it is; and we can’t begin to predict all of the possible mutations the virus could undergo, virologists told Live Science. The number of possible genetic mutations is greater than all the atoms in the visible universe, said Vincent Racaniello, a professor of microbiology and immunology at Columbia University in New York City. “A good fraction of the genome can be replaced.”

The coronavirus’s genetic code — made up of four different chemical bases or molecules that can be thought of as a four letter alphabet — is 29,881 letters long. Those letters provide instructions to make the 9,860 amino acids that are the building blocks of the virus’s proteins. When those chemical bases change, amino acids also change, which can affect the shape of the virus’s proteins; those shape changes, in turn, can affect how the virus functions, such as how it binds to human cells.

Previous studies on other RNA viruses — which like SARS-CoV-2 have a single strand of RNA as their genetic material — have found that more than half of the bases in these viruses can be changed, Racaniello told Live Science. Mathematically, that means that if a virus is 10,000 base pairs long, there are 4^5000 genetic sequence possibilities.


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