I'm not sure about that. Isn't there also a fine line where a virus becomes so deadly that it can no longer spread effectively before killing the host or becom

I'm not sure about that. Isn't there also a fine line where a virus becomes so deadly that it can no longer spread effectively before killing the host or becoming "harmless" yet spread much better and more effective than a deadlier version? I remember reading not long ago about a study that showed the common cold is so dominant that I can prevent covid from replicating in an infected person.