re: What purposes does the vaccine serve for people that have beaten covid?

Thank you for service. Unfortunately convalescent plasma (what you donated) hasn’t worked as well as we hoped. Likely for reasons suggested in the article you linked that circulating antibodies drop dramatically after four months. I think that’s the origin of his comment, though he likely misinterpreted it.

The title of the article you linked is a bit misleading. You will likely have bone marrow plasma cells for life. That does not suggest 100% immunity. Most of us have plasma cells to the chicken pox virus. However, that immunity wanes as we get older and once it drops below a certain level, that same virus comes back as shingles. With all that said, you will likely not get SEVERE disease if you’ve had COVID before. But it may not prevent you from getting a mild to moderate form of the disease. Vaccination after natural infection will almost certainly prevent that…the number of boosters if any however is TBD