Preliminary research from the US has suggested one particular mutation – G614 -has emerged in Europe and become dominant around the planet, leading the researchers to believe the virus has mutated to become more contagious.

The paper hasn’t yet been reviewed by other scientists and formally published.

The bold hypothesis, however, was immediately met with skepticism by many infectious-disease experts, and there is no scientific consensus that any of the innumerable mutations in the virus so far have changed the general contagiousness or lethality of covid-19, the disease caused by the coronavirus.

The researchers, from the Los Alamos National Laboratory in New Mexico, have been tracking changes to the “spike” of the virus that gives it its distinctive shape, using a database called the Global Initiative on Sharing All Influenza Data (GISAID).

They noted there seems to be something about this particular mutation that makes it grow more quickly – but the consequences of this are not yet clear.

“The mutation Spike D614G is of urgent concern; it began spreading in Europe in early February, and when introduced to new regions it rapidly becomes the dominant form,” the authors write. They describe the mutation “increasing in frequency at an alarming rate, indicating a fitness advantage relative to the original Wuhan strain that enables more rapid spread.”

The Los Alamos scientists’ goal was to set up an early-warning system for identifying potentially important mutations in the SARS-CoV-2 virus. Like all viruses, this pathogen makes mistakes when it copies its genetic material. But, much the way changing a single letter rarely affects the content of a book, most mutations don’t meaningfully affect the behavior of a virus.

The consensus has been that strains of the coronavirus are functionally the same, even if they look genetically different. The fact that the coronavirus is mutating is unsurprising, because all viruses mutate as they replicate. So far, this virus appears relatively stable, according to virologists, but the vast extent of the spread of the coronavirus has given it ample opportunity to evolve.

When the Los Alamos research team examined thousands of genome sequences uploaded to the Global Initiative on Sharing of All Influenza Data database, they identified several mutations that distinguished the version of the virus circulating in Europe from the version that originated in Wuhan; the Spike D614G mutation was among them.

When the mutated version arrived in northern Italy, an older and more susceptible population was unable to contain it. “It’s the fox that got into the henhouse,” Hanage said.

Hanage pointed to Washington state, where the virus was recognized relatively early and public health measures have proved effective at reducing cases. Both strains were circulating in the state by mid-March — and now, cases of both strains appear to be falling at the same rate. If the European strain really were more transmissible, he would expect it to crowd out all other versions.

One prominent scientist, Stanley Perlman, a virologist at the University of Iowa who played a role in naming the coronavirus, said Tuesday that the Los Alamos study looks credible.

“It certainly looks like it is more readily transmissible. Viruses mutate to become more transmissible, but not generally to become more virulent (unless this enhances transmissibility),” Perlman said in an email.

The research community is far from embracing any of the studies that haven’t gone through the rigorous peer-review process before publication in a journal. Hanage said people should view these pre-print papers skeptically, because the findings have not been reviewed and potentially challenged by other researchers.