(The Atlantic) – In truth, scientists were both right and wrong about the speed at which SARS-CoV-2 mutates. The rate of mutations as this virus jumps from person to person is indeed unimpressive. But scientists were not aware of a second, accelerated evolutionary track: When SARS-CoV-2 infects a single immunocompromised patient, it can persist for months, accumulating countless mutations in that time.

And if we are unlucky, that highly mutated virus might spread to others. This is the likely origin of Omicron, which appeared in fall 2021 with more than 50 mutations—an astounding evolutionary leap. Omicron looked like it had achieved four or five years’ worth of expected evolution in just months, Jesse Bloom, who studies viral evolution at the Fred Hutchinson Cancer Center, told me at the time. These mutations enabled Omicron to cause a massive wave of infections even among the vaccinated.

Scientists now believe that chronic infections in immunocompromised patients are a key driver of variants in Omicron and beyond. (Read More)