As the virus that causes COVID-19 traveled out of China and proliferated across the globe, it developed small mutations that accumulated into distinct versions of the virus. Scientists can now tell these versions apart by peering into the viral genome.
For example, here in the United States, there is the "West Coast" version of the virus that came directly from Asia, and a slightly different "East Coast" version which traveled through Europe.
But is one version of coronavirus more dangerous than the other? And should we be afraid of these new mutations?
The short answer according to virologists, is no.
Viruses are constantly copying themselves, so it's rather frequent that some of those copies will have mistakes, or mutations. These mutations are neither inherently good nor bad and are random.
So far, the novel coronavirus responsible for the global pandemic is mutating normally as virologists expected to see based on their experience with other similar viruses.
"Viruses mutate," said Dr. Nels Elde, Ph.D., associate professor of human genetics at the University of Utah. "That's one of the things that makes them such a successful entity."
"The word 'mutation' to people means something bad because it's got that connotation to it," said Dr. Vincent Racaniello, Ph.D., Higgins professor of microbiology and immunology at Mt. Sinai School of Medicine of CUNY.
"It simply means a change in the genome sequence. It doesn't mean that it's necessarily bad for you at all," Racaniello said. "Plants grow in the spring. Viruses mutate. It's no big deal."
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But as scientists across the globe learn more about these mutations, many have been eager to use these discoveries to decipher whether the virus is becoming more or less dangerous.
For example, in early March a group of scientists in China identified two different types of the virus, the L-type and the S-type. The L-type was found to be more widespread, leading to early speculation that the virus had evolved into a more infectious version of itself.
More recently, similar research out of Los Alamos National Laboratory in the United States which has not been peer reviewed identified a common mutation in the virus that began spreading in Europe in early February. The scientists suggested this mutation may have helped the virus spread faster and farther because it is inherently more infectious, generating breathless news coverage about a dangerous "mutant" virus.
But another group of scientists from Arizona State University arrived at a nearly opposite interpretation of the mutations they discovered. Their research led them to believe the virus might become weaker and die off, just like the 2003 SARS outbreak.
So far, the speculation about the virus' infectiousness are guesses, said Racaniello. He said there is no iron-clad evidence that these mutations have made any one version of the virus more contagious, deadlier or more resistant to potential therapies.
That's probably good news for humankind, because it means the vaccines and therapies being tested right now are likely to work against all known versions of the virus.
Scientists are actively monitoring the virus to see if it develops potentially dangerous mutations -- or even if it dramatically transforms into a new "strain" -- a word that has a very specific meaning to virologists but has also been used colloquially to describe the different versions of the virus that exist so far.
A new strain would signal a dramatic event, meaning the virus has mutated so much that it is "functionally different" than its predecessor, Elde said. According to Elde, virologists generally agree there is only one "strain" of novel coronavirus, although there are several versions of the virus in different parts of the world.
In fact, what scientists are observing, in terms of the differences between these viruses, is a phenomenon called viral "isolates," said Racaniello. That's when the genetic material develops slight variations that are not significant enough to make the virus behave in a totally different way.
These small changes happen frequently -- sometimes developing within the same person as the virus spreads throughout the human body.
"You can have different isolates from a single patient, by taking different samples from the respiratory tract and in the lung, for example," said Racaniello. "It does not mean the differences have any significance whatsoever."
"I think the bottom line is we don't really know right now whether mutation signals good news or bad news. It is somewhere in between," said Dr. Jay Bhatt, former medical chief at the American Hospital Association and an ABC News contributor.
"I think we will understand this better in the coming months."
What to know about coronavirus:
- How it started and how to protect yourself: Coronavirus explained
- What to do if you have symptoms: Coronavirus symptoms
- Tracking the spread in the U.S. and worldwide: Coronavirus map
Angela N. Baldwin, M.D., M.P.H., is a pathology resident at Montefiore Health System in the Bronx and is a contributor to the ABC News Medical Unit. Sony Salzman is the unit's coordinating producer.