• Influenza viruses mutate really rapidly, and those mutations can decrease a vaccine’s effectiveness. That’s one reason you can get reinfected with the flu over and over again — “and why we have to update vaccines every year,” says molecular biologist Kathryn Kistler, of the University of Washington, in Seattle. “The virus is evolving so much that our immune system no longer recognizes it.”

  • All of a sudden, it looked like SARS-CoV-2 not only was mutating but was doing so quite rapidly. Last month, Kistler and her colleagues at the University of Washington published a new metric to measure how quickly SARS-CoV-2 is evolving as it adapts to living inside humans. When Kistler first saw the value, she was shocked. “SARS-CoV-2’s rate of adaptation is remarkably high right now,” she says, “like roughly four times higher for SARS-CoV-2 than it is for seasonal flu.”

    Remember, the flu changes so fast that people can be vulnerable to it each year.

    “I don’t think SARS-CoV-2 will stop adapting,” Kistler says. “It may slow down, but viruses that evolve adaptively tend to keep doing that. They don’t tend to hit the limit of evolution.”

    This fast evolution has immense implications, many scientists say. It essentially dashes the hopes of eradicating SARS-CoV-2 in the U.S. or even in smaller communities. As with the flu, the coronavirus will likely be able to reinfect people over and over again. It will keep returning year after year.

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