The other part of why it’s hard for a pathogen to evolve to evade the vaccines is that they don’t just give us neutralizing antibodies. With mRNA and DNA vaccines in particular, which induce the host cell to manufacture spike protein inside the cell, there is likely also a strong response from the adaptive cell-mediated immune system. This is the coolest part of the immune system, because your cells effectively encrypt the antigens they encounter, and induce an adaptive T-cell response to anything that looks wrong (non-self) in the encrypted form. And the encryption key varies very widely among humans. So if spike mutates to evade one human’s cell-mediated immunity, that evasion strategy may not work for any of the next 10 humans it encounters. I dug up an old post I wrote about this here.