For months, scientists have debated whether a variant of the coronavirus that has come to dominate much of the world did so in part because it is more transmissible than other viruses.
On Thursday, a team of researchers reported new evidence that is likely to deepen the debate rather than resolve it, experts said; Too many uncertainties remain, in a pandemic that changes shape every day.
The new report, published by the journal Cell and led by researchers at the Los Alamos National Laboratory, suggested that the variant had such an advantage. Other researchers said the findings were not yet final.
The underlying question is as important as ever, both to understand the early stages of the pandemic and to anticipate how it will progress in the coming months. If the variant-defining genetic flaw, known as D614G, imparts even a slight increase in transmissibility, it would help explain why infections exploded in some regions and not others with density and similar attributes. Other experts argue that the variation is much more likely to spread widely by chance, multiplying outward from explosive outbreaks in Europe.
Viruses at Scripps Research, Florida, last month discovered that viruses with the D614G mutation were much more infectious than those without it, at least in cell culture. Those differences are necessary for further transmission to occur in the real world, but hardly sufficient; There is no evidence that variant D614G makes people sick.
The new paper, led by theoretical biologist Bette Korber, presents evidence in the form of laboratory findings, tests of infected patients, and extensive statistical analysis of the pandemic as the D614G variant repeatedly took over in cities, regions, and countries. “The consistency of this pattern was highly statistically significant, suggesting that the G614 variant may have an aptitude advantage,” the authors concluded.
In an interview, Dr. Korber said that all three lines of evidence “support the idea that it is likely to be a more communicable virus” than other variants. She added: “It is the dominant virus in the world, it only took about a month for that to happen, and now it is the one we should be looking at.”
The report also recognized that other alternative explanations were possible, including so-called founder effects, an advantage based on chance and on transmission dynamics in regions where the variant first took off. Other research has found no evidence of increased transmissibility for D614G, and for many scientists the question remains open.
“It is exciting to see a group take on the challenge of solving this, and the differences they report are interesting, particularly consistency across geography,” said Dr. Marc Suchard, biostatistician at the University of California School of Medicine, The Angels. . “But this is an extraordinarily challenging problem, evolution and demographics are complex, so there is much more work to do.”
Dr. Korber helped focus scientists’ attention on the D614G mutation in early May, when she published an article arguing that “when introduced to new regions, it quickly becomes the dominant form.” The new report expands on the previous one, and Dr. Korber said her group intended to continue their research testing different variants in animals, to see if differences in transmission are detectable.
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