Over time, epidemics can become ‘endemics.’ An epidemic is when there is a higher number of cases than we would expect, and an endemic is when there is a stable number of infections in the population.
For COVID-19 we’re still learning what a baseline worldwide will look like, but it doesn’t seem likely that we can eradicate it, so endemicity is more likely the future for COVID-19.
The build-up of immunity due to vaccination and infection drives the transition from epidemic to endemic. When this happens, new COVID-19 infections will mostly be in those people that have had the virus before, are vaccinated or were born after COVID-19 began.
It’s possible that protection against severe disease due to prior infection and/or vaccination will be long-lasting. That means that COVID-19 would be fairly mild for most people, as early childhood infections also tend to be mild. Of course, viral evolution and the new variants could complicate this.
More info on infectious diseases: https://www.health.nsw.gov.au/