I suspected spillback for Alpha because it had a bunch of intermediate mutations that were never seen in other lineages. But no animal reservoir was found and

I suspected spillback for Alpha because it had a bunch of intermediate mutations that were never seen in other lineages. But no animal reservoir was found and I now think the immunocompromised single patient explanation is more likely. I can see a patient that is known to have spending 6 months in a hospital bed not infecting anyone, because they are isolated and only seen by medical staff with serious protective clothing and masking. Then at some point someone slips up and it escapes. The article speculates that the animal reservoir could be rodents. If so, it's not sewer rats, at least not in one of the many countries that samples sewage to monitor outbreaks. https://journals.asm.org/doi/10.1128/mBio.02703-20 https://journals.asm.org/doi/10.1128/mBio.02703-20 By the way the transmissability of delta doesn't pose a hurdle for omicron. They are not competing, except in the sense that the severity of the delta wave makes people isolate and mask up.