Unless the vaccines have been completely bungled, there cannot be persistent spike production.

It's strands of mRNA that have been engineered to not replicate and to instruct cells to produce the spike protein. Because the strands can't replicate there is a finite number of cells that can produce spike proteins and once you hit that limit the spike production just stops.

Finite number of non-reproductive mRNA strands in a vaccine shot = finite number of spike proteins possible.

As for natural infection it stops when the infection has been eliminated.

Quick summary is that mRNA is very fragile and is simply a set of instructions on how to build a spike protein. The ribosomes read the mRNA and build the spike protein. Once it used the mRNA is quickly degraded and the body digests the pieces by macro****es. Just like we throw away the instructions after we build a large cabinet, the mRNA is now not needed and digested. This prevents cells from getting too big.

Once the mRNA is all used up, the body will stop making spike proteins, this will likely be within a day or two. Now as to how long the spike proteins will be in your blood will depend on your immune system. Your immune system will recognize that these proteins do not belong and manufacture antibodies to destroy them. This gives us the benefits of the vaccine. For most people with a healthy immune system they will likely all be destroyed within a week or two.

You can watch this video for an illustration as to how this works. We have previous studies with life spans of mRNA and proteins which should not be any different than the vaccine. They body treats mRNA and unwanted proteins the same. Doubt you will see too much data on this vaccines response as this information is pretty well known and does not really warrant the time and expense of a specific study. He lists many old studies in the comments of this video. Hope this helps you.



And FYI mRNA technology is not new. We have been working on this over 10 years with attempts to identify specific proteins unique to certain cancers.

Well, there's been a lot of work done in the area. In terms of production, they've worked for a long time at determining how protein production relates to the injections. There's aspects in how the code the mRNA itself as well as where you put it.

Here is a length review article that has some brief discussion about how they optimize protein production. It also goes on to talk about how delivery route matters.
https://www.frontiersin.org/articles/10.3389/fimmu.2019.00594/full

This one touches on delivery routes and protein production totals, along with where stuff goes, in mice.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4624045/

This one talks about one of the big coding aspects - replacing uridine with methylpseudouridine
https://rupress.org/jem/article/215/6/1571/42397/Nucleoside-modified-mRNA-vaccines-induce-potent-T

Here is the European Medicines Agency document for Pfizer, which talks about protein expression (of luciferase) and distribution on page 46 and 47, and again on 52 (talking about possible differences from spike to luciferase)
https://www.ema.europa.eu/en/documents/assessment-report/comirnaty-epar-public-assessment-report_en.pdf

A lot of that is summarized / wrapped up here, which is a super freaking cool rundown of the parts of the mRNA and what each does along with some of the "tricks" mentioned above (like the uridine sub)
https://berthub.eu/articles/posts/reverse-engineering-source-code-of-the-biontech-pfizer-vaccine/

Which is all useless until you do it in humans. Here is an actual study of circulating spike and S1 subunits after vaccination (Moderna). Its the only one I know of that directly addresses your question, and its super small.
https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciab465/6279075

However, it does support everything else - protein production for ~4 days, then its gone.

The S1 part of the spike is where the receptor binding domain is, and it cleaves off from the rest which stays stuck on the outside of the cell. The authors suggest S1 showing up means your body starts making the spike, then it goes away because your body stops making spike and the antibodies clear it. You don't get S1 after the second vaccination because you already have antibodies so your body is clearing it up. You do get full-length spike (S) sometimes, 15 days later. They suggest that's from your immune system responding and ultimately killing the cells expressing the spike, so some of the spike is released into the blood.

Maybe the last paper will give you some jumping off search terms or cited-by links to find a larger, similar study. If you do find something please share it, I am interested in this question as well.