"I believe that humanity has never previously developed immunity to a coronavirus previously"
That's not a testable hypothesis. If it has the virus will now be extinct and we'd be none the wiser.
We do, however, have several coronaviruses that cause mild diseases*. What's the nature of this interaction? Did they start off as equally lethal and evolve to respond to some sort of control from the host so as not to kill off the latter?
* And the current coronavirus, like others, is not lethal in its original host.
Biting the hand that feeds IT
