I'm not in a position to be familiar either with the mutated nucleotide sequences, nor the changes either in surface proteins or anything else, to know whether these changes
a) affect the spread
b) affect the cytokine response
c) will mean that infection with one great-grandchild strain or later, will confer immunity to other more dangerous strains.
I do remember reading that after the 1918 Spanish flu, there was a second subsequent wave, less deadly but still troublesome, the next year.
But the problem with the Spanish flu was the cytokine storm, *not* secondary bacterial infections.
Today's critter looks like it putters along for a week or two, then suddenly explodes in the lungs.
Some of the more unhinged online writings -- which you'll note I did NOT propagate -- said that this virus was spliced together as a biological weapon to ensure maximum spread, followed by a late fatal response. Hope that's not true.
I don't know the state of the art for sequencing that one can accurately predict the exact 3-D protein structure ab initio from the genetic sequence; still less the human immunological response.
Will continue to watch and pray.
Let us all remain vigilant and support one another.
4th generation is about person to person, i.e. First infected person to second to third to 4th. Speaking again to how transmissible it is.