By Peter Schelden
Even as the virus that causes COVID-19 continues to infect and kill across all habitable continents, the specter of a new and perhaps more deadly SARS-CoV-2 mutation looms over the horizon.
How worried should we be?
All viruses are prone to mutate. But RNA viruses like SARS-CoV-2 mutate more frequently than anything else in the world.
RNA viruses include a wide variety of familiar infections like:
Some estimates say RNA viruses account for up to 44% of all emerging infectious disease.
When a virus mutates, its new genetic changes usually cause it to be less harmful, or even harmless. But there is always a small chance that a mutation could cause a more harmful strain, which is what many researchers believe caused the Spanish flu of 1918 to become the deadliest modern pandemic.
Understanding Virus Mutations
Virus genes are not 'set' as they are for life forms like humans. They mutate so often that they are sometimes called a 'quasispecies,' in which a 'population of particles' infect a host that are nonidentical but related. The whole viral population may share roughly similar genetic traits, with a lot of variation, according to Vincent Racaniello, Ph.D., Higgins Professor of Microbiology & Immunology at Mt. Sinai School of Medicine of CUNY.
Sometimes mutations cause serious difficulties in treating or inoculating people from infection, or it can provoke more dangerous versions of the disease. Some of these problems have sometimes occurred in HIV, hepatitis C, and measles, which are all caused by RNA viruses, as is COVID-19, the novel coronavirus.
But virus experts say that even if a mutation causes a death rate increase, this does not necessarily make a virus more deadly overall. Killing your host quickly can make it hard to spread to a new one, and natural selection often prevents viruses from becoming more deadly as they mutate.
In fact, mutations often prevent the virus from successfully spreading, or lead to a weaker version of the original. Scientists hunt for weak replicants of viruses for their potential as vaccine strains.
How COVID-19 Mutations Compare to Other RNA Viruses
All viruses mutate at different rates. More than 25 RNA viruses have been measured in labs, with individual viruses counted for mutations. Scientists have found that anywhere from one in ten thousand to one in a million RNA virus particles contains a mutation, depending on the type.
Here are some mutation rate estimates for other known viruses. This number tells you roughly how many viral particle mutants will exist in a given viral population:
- Influenza A: 319/10,000,000, (.00319%)
- Human Immunodeficiency Virus (HIV): 9,927/100,000,000 (.009927%)
- Measles: 9/100,000, (.009%)
- Poliovirus 1: 3/10,000 (.03%)
This does not tell the whole story about a virus' potential to mutate, but it offers a rough idea of how easily and often they do.
COVID-19 is not as well-studied as these other diseases. But an estimated range of its mutation rate has emerged from a study of 30 publicly available samples of SARS-CoV-2. Researchers at Johns Hopkins estimate the mutation rate of COVID-19 at:
- COVID 19: 21/20,000 (.00105%) to 63/50,000 (.00126%)
What We Know About COVID-19 Mutations
The facts about COVID-19 are being reinterpreted with better understanding every day. An early study that claimed the existence of a supposed "strain S" and "strain L" of the virus that causes COVID-19 was published March 3. It claimed to identify one strain in China that had become more aggressive than the other.
But that study was widely criticized for exaggerating the significance of its claims, as well as for using a small sample pool.
A mutant variation of the COVID-19 virus that causes additional concern has yet to be found, according to researchers. This is based on the known mutations of SARS-CoV-2, which number over 100.
"Different clades (evolutionary descendants) emerge as viruses evolve," says one Johns Hopkins study. "This is entirely normal and does not mean there are new strains of SARS-CoV-2 that are more pathogenic than others circulating right now."
That doesn't mean scientists aren't interested in how COVID-19 mutates. In addition to searching for weak mutations that might serve as vaccines, researchers can track the spread of the disease by following its mutations. This can help us know where new infections are coming from, among other important details about the novel coronavirus.