[q1w2]

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.

[rrock]

The polyA tail is in the 3′ UTR (after the stop codon) and is not translated. It doesn’t appear in the final protein sequence. It’s also a fairly standard feature.

[q1w2]

To be clear, it's not translated into the final antibody, but it remains present in the vaccine, and hence in your body - it is what gives the vaccine structural stability in the body.

...and yes, it is standard - it is not covid-vaccine specific.

This is all covered in This Week in Virology - one of the recent episodes about 3 months ago.