I think I’m starting to grok this.
Nutshell version is something like this: In a manner roughly analogous to what happens with someone with a bacterial infection stops taking antibiotics early (and therefore allows for some small amount of resistant bacteria to survive and thrive), mass vaccination during a pandemic will breed inevitably breed a super-covid.
Ish. There’s way more to it than that, and part of it has to do with the fact that the mRNA based vaccine technology is fundamentally different from what we have historically thought of as “vaccines”. mRNA was able to be deployed quickly because it is laser-focused on a single protein. Which makes it, in a manner of speaking, an easy bullet for the virus to dodge.
What I think Vanden Bossche is saying is something like “Never mass-vaccinate during an active pandemic, and REALLY never mass vaccinate with mRNA based laser-beam vaccines during an active pandemic”.