You see the poly(A) sequence at the end? That is what stabalizes the entire structure so that it doesn't denature. I called it a "base", but you are right that it's not adding to the size of the overall structure much.

The point is that the normal virus protein obviously doesn't have that - it's human design to create stability.

My point was that there are not billions of covid spike proteins floating around the human body when you get the vaccine.