Reinfection might also be because of the four lines of rna code that was copied pasted from different sources. For example, the coronavirus uses the ACE receptor to invade lung tissue. Over time you build up immunity but the virus of course is always in you now in very tiny amounts. Just kept under control by immune system. Then over time a mutation occurs to allow the CD147 receptor to be infected through a different enhancement of a spike protein (pinballing). Now it infects red blood cells and you collapse a few days or weeks after being cured.