The very end of the article touches on that subject:

Still unknown is whether this mutant virus could account for regional variations in how hard COVID-19 is hitting different parts of the world.

In the United States, doctors had begun to independently question whether new strains of the virus could account for the differences in how it has infected, sickened and killed people, said Alan Wu, a UC San Francisco professor who runs the clinical chemistry and toxicology laboratories at San Francisco General Hospital.

Medical experts have speculated in recent weeks that they were seeing at least two strains of the virus in the U.S., one prevalent on the East Coast and another on the West Coast, according to Wu.

“We are looking to identify the mutation,” he said, noting that his hospital has had only a few deaths out of the hundreds of cases it has treated, which is “quite a different story than we are hearing from New York.”