The mRNA vaccines (Pfizer or Moderna) and the DNA vaccines (J&J and Astra-Zeneca) supposedly only generate spike proteins in the body. The DNA based vaccines do use an adenovirus vector to get spike DNA into to nucleus, but it is stated by the DNA companies that the adenovirus has be modified to not be able to replicate itself, so the only product is supposed to be the spike protein. (The mRNA vaccines do not use a virus vector, but rather some sort of synthetic delivery system, like a liposome.) The following discussion is based on these assumptions (even though they may being lying to us!).

There is no known mechanism by which the spike protein, or any protein for that matter, can replicate itself in the body. There is no "reverse ribosome" that would take a protein and cause its corresponding mRNA or DNA to be generated from it. Thus, if you ingest the spike protein that sheds from vaccinated people, you will not be generating more of it in your body, and thus you are very unlikely to spread it effectively to third persons. But since so many people are getting vaccinated, many people will pick up some spike protein from them, so third-person spread doesn't really matter to the evil agenda.

One problem with spike protein is that it has peptide domains resembling prions. It is speculated that these domains might be bio-active and be able to cause classic prion disease. You don't need need a lot of bio-active prion molecules to cause prion disease, because prions are like seed crystals. Once a prion initiates formation of an amyloid plaque, the plaque starts accumulating more plaque material on its own, like a growing cryatal, without the prion. The amyloid plaques, which are composed of mis-folded versions of natural proteins already present the body, can then accumulate in organs such as the brain and elsewhere, causing pathology.

There are other mechanisms by which spike protein might cause pathology, such as its ability to bind to ACE receptors, but I haven't looked into that enough about that to go into it here.