A story published this week in the Los Angeles Times warned of a dominant mutant strain of Covid-19 that could be more contagious than the one that's had much of the country on lockdown since early March. The strain could make people who've already had Covid-19 more vulnerable to reinfection.
Because the news report in the LA Times was based on emerging research on viral mutations that have not yet been peer-reviewed, scientists were quick to scrutinize the idea that a single mutation is causing fundamental changes to the way the virus behaves.
That doesn't mean that the virus isn't mutating — it is. But many experts say this mutation doesn't mean that people are in any more danger, at least, not yet.
Why do viruses mutate?
Stephen Goldstein is an evolutionary virologist who studies coronaviruses at Utah University Health. He tells Inverse there's no evidence that any variants of SARS-CoV-2 are more contagious or lethal than others. (SARS-CoV-2 is the virus that causes Covid-19.)
“To say that this single mutation is going to make people able to get reinfected or make a vaccine ineffective is getting way out ahead of where the data is,” Goldstein says.
The idea that certain mutant strains will drastically affect the course of the pandemic isn’t supported by current data, Goldstein says. He also describes that claim made in the study as "unwarranted and irresponsible."
"Unwarranted and irresponsible."
Lucy van Dorp, a researcher at the University College London Genetics Institute, argues the term “mutant strain” has misleading connotations. On Tuesday, van Dorp and her team published a peer-reviewed study in the journal Infection, Genetics, and Evolution which analyzed how SARS-CoV-2 is mutating.
Van Dorp's team found 198 recurrent mutations after studying the genomes of 7,500 people infected with Covid-19.
“All viruses mutate,” van Dorp tells Inverse. “It is important to keep track of changes in the genome of the virus, but detection of a single change at high frequency is not sufficient alone to say a strain has become more contagious, transmissible or virulent.”
Mutations can happen each time a virus's genetic sequence is copied. Coronaviruses (which depend on an enzyme called RNA polymerase to replicate) tend to mutate more rapidly and are more error-prone than other viruses that use DNA polymerase, Goldstein says.
"They make mistakes; they're sloppy but there's a benefit to that for the virus," he says. Replicating quickly gives the virus genetic diversity, which can help it spread farther within a population.
Importantly, mutations don't necessarily increase the potential harm of a virus or have clear downstream effects on infected people.
Is there a new strain of coronavirus?
"All viruses mutate when they replicate and most of these have no impact on the behavior of the virus," van Dorp explains. "There is currently no compelling evidence that any one mutation has changed the virulence or transmissibility of SARS-CoV-2."
The pre-print of the controversial study, which is hosted on the preprint server bioRxiv, is based on a computational analysis of more than 6,000 coronavirus sequences from around the world collected by the Global Initiative for Sharing All Influenza Data.
That team found 13 different mutations near the virus' the spike protein (a major player that facilitates the virus' invasion of human cells).
In turn, the team identified one seemingly dangerous offender, called D614G. That's what's described as the dominant mutant strain.
According to the report's authors, D614G is of "urgent concern," as it may increase transmissibility — how the virus spreads within a population — and the severity of Covid-19. The study shows D614G has dominated Europe, North America, and Australia, and should be considered a central target by researchers chasing an effective vaccine.
(The report's lead author, Bette Korber, a well-known computational biologist at Los Alamos National Laboratory, did not respond to repeated requests for comment.)
It's too early — Every virologist Inverse consulted says it's too early to claim there's a new dominant strain of the virus that will shape the direction of the pandemic.
“Any claims and papers that say 'we've identified this mutation that has this impact' should be taken with the world's biggest grain of salt," Goldstein says.
"...The world's biggest grain of salt."
William Hanage, an epidemiologist at Harvard University, raises the possibility that oddities in reports of SARS-CoV-2 genome sequences, especially those found in preprints rather than peer reviewed articles, may be related to sequencing errors from different sequencing technologies. Other scientists published similar concerns and potential technical solutions May 5.
Meanwhile, van Drop notes that the spike in D614G seen "may have occurred by chance and just happened to go up in frequency as the virus spread in Europe."
The future of mutant strain science — Meanwhile, van Dorp's new study — an analysis of 7,500 people sick with Covid-19 that shows 198 recurrent mutations in SARS-CoV-2 — does not suggest the virus is mutating faster or slower than scientists would expect given historical data about coronaviruses.
Her study also doesn't speculate whether the virus is becoming any more, or any less, dangerous.
Van Dorp says the team was careful not to "overinterpret" the role of single mutations in their study.
"This [compared to the other study] is much more measured while covering much the same ground — but in a more responsible fashion," Hanage tells Inverse.
Mark Slifka, a microbiologist at Oregon Health and Science University, says the controversial study should be viewed with "caution until more information on biological significance has been attained."
Goldstein says that while a mutation might make one specific type of antibody less effective, it doesn't wipe out the immune system and leave one unprotected.
"Your immune system is far too complex, multifaceted, and well evolved, generally, to be quite so easily defeated," Goldstein says.
There's also some comfort in the fact that once we have an effective vaccine platform, tweaking the tech to adapt to a particular mutation is relatively easy, Goldstein says. Scientists do that every year while developing the flu shot.
Taken together, the emerging data shows SARS-CoV-2 is changing. How these changes will influence the search for effective treatment or a vaccine, or shape the course of Covid-19 pandemic, remains to be seen.
Scientists won't understand the power of certain mutations until they conduct studies where some animals or humans are infected with mutant strains, others are infected with the original strain, and both groups are observed.
But for now, any mutant strain isn't a reason to become more afraid of Covid-19.
"Physical distancing is what has the potential to hopefully help us keep a lid on things until we have a vaccine," Goldstein says. "There are no mutations that are going to happen to make this virus overcome good public health practices."
Correction, 9:48 p.m. Eastern, May 6, 2020: A reporting error on our part incorrectly stated Bill Hanage's opinion on the pre-print. We have corrected our story above. Inverse regrets the error.