Lvs is mostly wrong. I am not claiming any of these mutant strains are attenuated, I am saying that deletion mutants exists and we should investigate them to see if they are attenuated.
I am not providing evidence that an attenuated strain exists, just evidence that it could exist because the right type of mutations are found in SARS-CoV-2. The only way we are going to find out if there are attenuated strains is to look for them which as far as I know nobody is trying.
So let's remember how evolution works, shall we? Evolution selects for strains that reproduce the most and selects against ones with attenuated reproduction rates. That's the whole basis of biology. If you've observed a wild strain sequenced in a database, that should be considered direct evidence that it reproduces well enough to have been sampled as a representative isolate.
> as far as I know nobody is trying
Of course we are. We are deeply engaged in studying the key residues that mediate all aspects of viral infection, reproduction, and clinical pathology. That's another way of saying that an incredible number of researchers have dropped everything to study the genetic and molecular determinants of pathogenicity. Don't worry -- we are on it.
I am not providing evidence that an attenuated strain exists, just evidence that it could exist because the right type of mutations are found in SARS-CoV-2. The only way we are going to find out if there are attenuated strains is to look for them which as far as I know nobody is trying.