May 8, 2020

Is there a more contagious strain of the new coronavirus? Experts are skeptical.

Daily Briefing

    A study, not yet peer-reviewed, published last week on the preprint server BioRxiv suggests that a mutated, more-contagious strain of the new coronavirus has been spreading since early February—but many experts are skeptical of the study's claims.

    Cheat sheets: Evidence-based medicine 101

    A new strain of coronavirus?

    For the study, a team of researchers from the Los Alamos National Laboratory led by Bette Korber, a computational biologist at the lab, looked at mutations that affect the so-called "spike" of the new coronavirus, which is a protein on the surface of the virus that allows the pathogen to recognize host cells. The researchers honed in specifically on one mutation, known as D614G, which can change one molecule within a virus' spike and alter the shape of the protein.

    The researchers in the study claim they found that a strain of the new coronavirus with the mutation, called the G lineage, emerged in February. The researchers state that while the G lineage strain was fairly uncommon in early March, it was the dominant strain of the new coronavirus that was circulating in most of Australia, Europe, and North America by April. Further, the researchers say strains of the new coronavirus without the mutation—called D lineage strains, which include those that first emerged in Wuhan, China—have become less common.

    The researchers said they published the study before it was peer-reviewed because they felt an "urgent need" to provide "an early warning" about the G lineage strain. The researchers said their findings could affect the development of vaccines against the new coronavirus and drugs intended to treat Covid-19, the disease caused by the virus.

    According to the Los Angeles Times, Korber in a Facebook post regarding the study wrote, "The story is worrying, as we see a mutated form of the virus very rapidly emerging, and over the month of March becoming the dominant pandemic form." She continued, "When viruses with this mutation enter a population, they rapidly begin to take over the local epidemic, thus they are more transmissible."

    Experts are skeptical of study's claims

    Experts have said the researchers' claims that a G lineage strain of the new coronavirus exists and is more transmissible than the D lineage strains are plausible. However, many experts have noted that the researchers' study doesn't prove those conclusions.

    Some experts have said, at this time, they don't believe the new coronavirus has mutated enough to form a completely different strain of the virus.

    "I think the majority of people studying [coronavirus genetics] wouldn't recognize more than one strain right now," Charlotte Houldcroft from the University of Cambridge said.

    According to The Atlantic, that's because coronaviruses typically mutate slowly—at a tenth of the speed of influenza viruses, which commonly have multiple strains. Houldcroft explained, "This is still such a young epidemic that, given the slow mutation rate, it would be a surprise if we saw anything this soon."

    And although the new coronavirus has picked up a number of mutations since it first emerged in 2019, it hasn't experienced more mutations than scientists would expect at this point, The Atlantic reports.

    Nathan Grubaugh from the Yale School of Medicine said, "There's nothing out of the ordinary" with how the new coronavirus is behaving.

    Further, experts have said while it's possible that the D614G mutation could make the new coronavirus more transmissible, which could explain why the G lineage has become more dominant, it's also possible that the mutation has no effect on transmissibility and the G lineage has become more dominant by chance, The Atlantic reports.

    Sergei Pond, an evolutionary biologist at Temple University, said the new study doesn't "provide evidence to claim transmissibility enhancement. In order to establish this, you'd need direct competition between strains in the same geographic area."

    "[T]he conclusions are overblown," Lisa Gralinski, a scientist who specializes in coronaviruses at the University of North Carolina, said. "To say that you've revealed the emergence of a more transmissible form of [the new coronavirus] without ever actually testing it isn't the type of thing that makes me feel comfortable as a scientist."

    But Gralinski said figuring out which mutations affect the behavior of the new coronavirus isn't a priority at this time. Instead, researchers are focused on developing a vaccine against the virus and treatment for Covid-19, and they likely won't start looking into the virus' mutations until that "urgency has waned."

    Grubaugh said determining whether the new coronavirus has mutated and its behavior has changed ultimately won't affect public health measures intended to control the virus.

    "Identifying a mutation that does something different doesn't really change our response," he said. "It just creates a diversion from what we need to be focusing on" (Yong, The Atlantic, 5/6; Vartabedian, Los Angeles Times, 5/5; Zimmer, New York Times, 5/6).

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