The problem with stories about dangerous coronavirus mutations. There’s no clear evidence that the pandemic virus has evolved into significantly different forms—and there probably won’t be for months

From the article:

As an epidemic progresses, the virus family tree grows new branches and twigs—new lineages that are characterized by differing sets of mutations. But a new lineage doesn’t automatically count as a new strain. That term is usually reserved for a lineage that differs from its fellow viruses in significant ways. It might vary in how easily it spreads (transmissibility), its ability to cause disease (virulence), whether it is recognized by the immune system in the same way (antigenicity), or how vulnerable it is to medications (resistance). Some mutations affect these properties. Most do not, and are either silent or cosmetic. [...]

There’s no clear, fixed threshold for when a lineage suddenly counts as a strain. But the term has the same connotation in virology as it does colloquially—it implies importance. Viruses change all the time; strains arise when they change in meaningful ways.

New strains of influenza arise every year. These viruses quickly acquire mutations that change the shape of the proteins on their surface, making them invisible to the same immune cells that would have recognized and attacked their ancestors. These are clearly meaningful changes—and they're partly why the flu vaccine must be updated every year.

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This isn’t to say that the Los Alamos study is bad or wrong—it comes from a respected team and presents interesting data. But the evidence it provides cannot distinguish between two equally plausible explanations—that the G-viruses were more transmissible, or that the G-viruses were just lucky.

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The bottom line: It will take time to know whether different strains of the new coronavirus even exist, let alone whether any are more or less dangerous than the others. Any claims of that kind should be taken with a grain of salt for the next several months, if not longer. “In the short term, it’s highly unlikely that we’d be able to define new strains,” Wasik says.