[sterlind]

It might require the full spike protein, not just the receptor binding domain which is what the mRNA vaccines include.

Also, I'm not sure how the coronavirus proper gets into the brain, but it seems likely it's through infecting some cell that crosses over, rather than directly getting past the blood-brain barrier. That's less relevant for the mRNA vaccines because A) mRNA doesn't replicate and B) the spike proteins that get produced mostly get chopped up before they can leave the cells (they're not budding off into viral envelopes after all.)

Also, nearly everyone in the world has had the real thing now - that's a lot more spike than the vaccines contain, orders of magnitude more.

[Vecr]

Both the Pfizer-BioNTech and Moderna vaccines use a full length spike, look at the WHO definitions for elasomeran (Moderna) and tozinameran (Pfizer). For example, the Pfizer-BioNTech vaccine is described as "messenger RNA (mRNA) 5'[prime]-capped, encoding a full-length, codon-optimised pre-fusion stabilised[sic] conformation variant (K986P and V987P) of the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2, GenBank: MN908947.3) spike (S) glycoprotein, flanked by 5'[prime] and 3'[prime] untranslated regions and a 3'[prime] poly(A) tail; contains N1-methylpseudouridine instead of uridine (all-U>[methylpseudouridine symbol]). immunological agent for active immunization (anti-SARS-CoV-2)". It's clearly full length, Pfizer abandoned their RBD-only candidate.

[sterlind]

Ah, thank you for correcting me.