What the theory of "Evolutionary Dynamics of Viral Attenuation" implies is that a lot more people were dying of colds when it first entered the human race.

There is also mathematical evidence that compares the probabilistic error rates of COVID replication to the amount of mutations already encountered and it is looking good for us. COVID mutation rates are very high and most if not all have been encountered in humans. While some resist anti-bodies better it appears that none will do so entirely and thus COVID will devolve to a "common cold" as humans themselves are selected out (multi-generationally) for higher amounts of resistance.

It's basic biology in action.

It is important to remember that almost all diseases work this way (possibly ALL diseases if we could morally afford the extremely high death rates of some of them e.g., a 99.9% death rate for some diseases like rabies).

See sibling response, but also the answer to your question is “more than you would probably think”:

https://jcm.asm.org/content/48/8/2940

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4181476/