Seasonal coronavirus protective immunity is short-lasting

Antibodies wane, but B-cell and T-cell response is important for longer term protection. Fortunately, we have results (including [B] and [T]) that vaccines also induce these memory cell responses. Also, the durability of immunity from coronavirus probably depends on the exact coronavirus. It does seem to be true for SARS, but possibly less so for the seasonal coronaviruses that cause a respectable fraction of common colds[3]. We don't really know yet where SARS-CoV-2 falls on that spectrum. [B]: https://www.medrxiv.org/content/10.1101/2021.07.12.21259864v... [T]: https://www.medrxiv.org/content/10.1101/2021.06.30.21259787v... [3]: https://www.nature.com/articles/s41591-020-1083-1

Saying that coronavirus infections in general produce long-lasting immunity is too strong, I think. For non-SARS coronaviruses (e.g. HCoV-OC43), immunity seems to drop off within a year: https://www.nature.com/articles/s41591-020-1083-1

Meanwhile this study about human coronaviruses tells the exact opposite story: https://www.nature.com/articles/s41591-020-1083-1 A group of Dutch clinicians have been taking blood samples from a cohort of people for 30 years now (it started out as a project to study AIDS/HIV) and measured antibody levels against the other human coronaviruses. They find that people get re-infected after a year or so. There's no reason to believe that the immune system should behave any different towards COVID-19. Given the US government's past track record on the pandemic, right now I'm disinclined to trust the CDC.

This also assumes that acquired immunity from an infection is complete and permanent. Immunity to other coronaviruses decays over a year or two -- meaning that before the five years are up in your scenario, there would be a significant cohort of prior victims open to reinfection. See, e.g., https://www.nature.com/articles/s41591-020-1083-1