Once a vaccine is found it will only SUPPRESS it won't ERADICATE the disease. This virus is never going completely away. Depressing?

It’s extremely hard to completely eradicate a virus.  We’re pretty sure that we’ve eradicated the virus that causes small pox (99.9%).  COVID, like every other virus, will probably be around forever.  The virus (or a descendant thereof) that caused the Spanish flu still exists.  You are inoculated for it in your yearly flu shot.  It’s possible that COVID is not the only cause of what we see around us today.  It, much like the virus that caused the Spanish flu, may allow other “bugs” to get a better hold in us (weakens our defenses.   Viruses also mutate. They, like any other organism, will do whatever it takes to survive. 

It's not a matter of being "smart".

Micro-organisms don't have brains, but they respond chemically to their living-conditions, and if they survive attack somehow adjust themselves to cope better. How, I do not know - I am not a micro-biologist.

Some adapt more readily than others, which is why the common-cold is not curable or will not yield to vaccines, and influenza is not much more curable.

Once a pathogen finds a home in humans it won't go away. It's not only the 1919 Influenza virus Shuhak cites that is still around. So is the  bacteria responsible for the Black Death, and it does make its presence known occasionally.