Goody, all valid points. Another thing to consider is is the effects to lungs, previously damaged or not, can leave long lasting effects. This applies to young and old alike. Research in the UK suggests the lungs of coronavirus survivors could return to "apparently normal" after six months with minimal issues — like a weakened ability to exercise — those who go on to develop ARDS could "take as long as 15 years for their lungs to recover," according to FIMC (Faculty of Intensive Care Medicine the UK's professional body for intensive care doctors and practitioners). Surely, that is one research body's study. Others have suggested low oxygen levels experienced in CV19 patients blood causes other effects on organs and brain tissue. Remember it takes many days to a couple weeks to recover.
In it's current form the virus tends to effect infirm people the most. Mutations can occur when there are large numbers of people contracting the disease, and also as the virus begins to taper off from it's peak when it goes through genetic change within itself to proliferate again.