As the coronavirus swept across the world, it picked up random alterations to its genetic sequence. Most of those mutations made no difference in how the virus behaved.
But one mutation near the beginning of the pandemic did make a difference, multiple findings suggest, helping the virus spread more easily and making the pandemic harder to stop.
The mutation, known as 614G, was first spotted in eastern China in January and then spread quickly throughout Europe and New York City. Within months, the variant took over much of the world, displacing other variants.
Scientists have been fiercely debating why. Researchers at Los Alamos National Laboratory argued in May that the variant had probably evolved the ability to infect people more efficiently. Many were skeptical, arguing that the variant may have been simply lucky.
But a host of new research — including close genetic analysis of outbreaks and lab work with hamsters and human lung tissue — has supported the view that the mutated virus did have a distinct advantage, infecting people more easily than the original variant.
There is no evidence that a coronavirus with the 614G mutation causes more severe symptoms or kills more people. But the subtle change in its genome appears to have had a big ripple effect, said David Engelthaler, a geneticist. "When all is said and done, it could be that this mutation is what made the pandemic," he said.
The first outbreaks would have spread around the world even without the mutation, most researchers say. It was already highly contagious, Engelthaler said.
But the mutation appears to have made the pandemic spread farther and faster. One study found that outbreaks in the United Kingdom grew faster when seeded by the 614G variant. Another said hamsters infected each other more quickly when exposed to the variant. And in a third, the variant infected human bronchial and nasal tissue in a cell-culture dish far more efficiently than its ancestor.
Kristian Andersen, a geneticist, believes the difference is subtle. Even so, he said the variant's higher transmissibility could help explain why some countries that were initially successful in containing the virus became susceptible to it later. The virus may have been "harder to contain than the first time around," he said. "Don't necessarily expect that the enemy of two months ago is the enemy you have the next time."
