@jayctoy
Vaccines are biological agents that elicit an immune response to a specific antigen derived from an infectious disease-causing pathogen. That's it. The agreed definition for nigh on 200 years. Other properties of any specific vaccine are irrelevant with respect to whether it's a vaccine or not.
The spike protein can cross into the bloodstream, although most appears to end up in the lymph system. There are Rat studies that show the vaccine produced S1 protein crosses the blood brain barrier, but follow-on studies In Vitro using cultured endothelial human cells showed it did not. So it may, it may not, we can't experiment on a bunch of humans to find out. There is significant data showing that SARS-CoV-2 can cause brain inflammation, and it's been hypothesized that the spike protein may be involved, but I have not seen definitive data on that. Not saying there's none out there.
The lipid 'bubble' encapsulating the mRNA is highly unstable - hence the onerous storage requirements - and once liberated, the mRNA is quite unstable as well. So spike protein not phagocytized by lmphocytes triggered by it, is unlikely to have much residence time in the body anyway. My hunch - and it is not based on reviewed data - is that folks that would have a massive response to the vaccine (such as you and other seem to fear) would be those likeliest to die from a COVID infection. Making the vaccine an even better risk.
But no drug or vaccine is without some risk, and some side effects. It's a risk/benefit calculation. The selfish consider only themselve in that calc, people that aren't, consider their fellow citizens as well.
