If the virus isn't evolving (I'm taking this from your comment of being reinfected over and over which implies the same virus), where's the possibility of vaccine escape (notwithstanding that no vaccine is 100% )effective?
No, you have misunderstood, @Winederlust. The virus is constantly mutating. Immunity from both the vaccine and infection wanes over time. Neither vaccination nor natural immunity from infection provide sterilising immunity, only partial immunity, you can still be infected by the virus but you may well be asymptomatic or the symptoms will be less severe.
Currently, it's estimated that 90+% of the UK population (93% in England and Scotland, 91% in Wales and NI) has antibodies against SARS-CoV-2.
www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/articles/coronaviruscovid19latestinsights/antibodies
The effect of that is that transmission slows down and if people who have immunity are infected, most of them will not be seriously ill. As immunity wanes over time, transmission will increase until immunity levels go up enough to slow transmission again. We are reaching the point of endemic equilibrium, where the number of people infected at any one time stays the same because every time someone's immunity wanes, somebody gets infected and develops immunity IYSWIM? Or you get shallow waves. So things stay at a constant level (probably not much better than it is currently in terms of cases/fatalities as you can't get much better than 93% of the population having antibodies) or it is like flu/norovirus season, there is a peak then a trough.
In terms of disease severity, unless the virus mutates to be less virulent, things will be as they are now, some people will still become seriously ill.
However, there do seem to be some interesting developments in treatments for COVID-19, which will make a huge difference.