[mlyle]

Many reasons, that I don't fully understand. A few are: adjuvant properties of the vaccine, and the fact that there's a booster dose given, and that there's a whole ton of spike protein made and not many other targets.

But the reasons don't really matter -- studies like https://www.nejm.org/doi/full/10.1056/NEJMc2032195 have shown those vaccinated have significantly higher neutralizing antibody titers in their plasma than convalescent plasma, and slow decay of this response.

Of course, this isn't perfect evidence, as it is just the neutralizing antibody responses and the adaptive immune system response is much more complicated than this single measure.