How Viral Mutations Occur in SARS-CoV-2

Since the beginning of the COVID-19 pandemic, scientists knew it would only be a matter of time before new variants of SARS-Cov-2, the virus that causes COVID-19, began to emerge.  

That’s because mutations always arise as viruses spread. And, we know all too well that SARS-CoV-2 has spread quickly throughout the world.  

This particular virus gains access to our cells using its “corona”—a layer of protein spikes that fits into our cellular receptors like a lock and key. But, says Akiko Iwasaki, PhD, a Yale immunobiologist and leading COVID-19 researcher, “When viruses enter the host cells and replicate and make copies of their genomes, they inevitably introduce some errors into the code.” Iwasaki, who studies the mechanisms of immune defense against viruses, compares the changes introduced by these errors to a faulty spell-checker.  

Some of the random errors passed on are either neutral or detrimental to the virus. But some errors are beneficial, making it more contagious. Over time, the cumulative effects of these mutations may be enough to change how the virus behaves. These “better-fit” versions of the virus become the “building blocks of selection,” says Nathan Grubaugh, PhD, a Yale School of Public Health epidemiologist.  

These constellations of viral mutations—known as variants—may take hold if there is evolutionary pressure for them to do so. But the novel coronavirus is highly contagious and has spread almost unchecked throughout the world for the last year. It remains a bit of a mystery as to why these variants are emerging now—and what it will mean long-term for vaccination programs.  

Currently, scientists are optimistic that the two mRNA vaccines available in the U.S.—Pfizer-BioNTech and Moderna—will continue to provide protection. “There are certain mutations in some of these variants that seem to decrease the effectiveness of really important antibodies,” says Grubaugh. “But luckily with vaccines, you don’t just create one antibody—or two or three—you create many different antibodies that recognize different parts of the virus.”  

“The mRNA technology is very flexible and can accommodate new mutations,” says Iwasaki. And even if the effectiveness of vaccines dropped to, say, 75 or 85%, that would still provide important protection and prevent severe cases of the COVID-19 from occurring.  

In this video, Iwasaki and Grubaugh discuss the science behind the SARS-CoV-2 mutations and explain why it’s important to continue wearing masks, avoiding crowds, and washing your hands.  

“We have all the tools needed to stop the spread of these new variants,” Grubaugh emphasized. “If we all put effort into doing our part, these variants won’t be able to take a foothold in our community.”