1) Many people who are infected by COVID-19 are asymptomatic. Is it possible that the vaccine could fail to produce the desired immune system response in such people. That is, assuming their cells produce harmless spiky crowns as specified by the mRNA, might their immune system simply ignore them?
This is a good point. I don't think we know anything about how people will respond to the vaccine that have been previous infected with the virus. I'm pretty sure these people were excluded from the initial trials and are too far down the cue to have been vaccinated en masse to study.
Best case scenario, the vaccine improves upon natural immunity by prolonging immune memory. Worst case, the vaccine reprograms natural immunity and turns a normally well tolerated response into a harmful one. My professional opinion is the former is highly likely, while the latter is not without precedence (albeit one vaccine in the history of vaccination).
We'll know the answer to this question in due time.
2) What mechanism eventually stops my cells from producing those spiky crowns? Does the vaccine change the cells or simply give them one-time-use instructions?
It should be noted that this question refers to only one (mRNA) of the many formulation of the COV2 vaccine. If the novelty mRNA vaccine is a major hang up for you, you have access to more traditional forms of the vaccine (e.g. Astrozenaca).
The reason spike proteins won't stick around forever is due to the instability of RNA. In fact, RNA is one of, if not the most highly unstable biomolecules. Thinking about this from the perspective of the central dogma of biology is probably the easiest way to understand why RNA is so unstable. DNA is trascribed into RNA, and RNA is translated into protein. In other words, RNA is an intermediate step between gene blueprints (DNA) and the functional form of a gene (protein). This affords a powerful opportunity for RNA to regulate protein production through a variety of means that hinge on the stability of RNA. Instability is the default, and stabilizing RNA is an active process. Thus, RNA is quickly degraded in the absence of a cell's highly coordinate attempt to stabilize it.
3) Do we need more long term data to show the vaccine is safe? This is very new technology (mRNA vaccines have never been rolled out before). I'm not sure how to best refine this question, so I will leave it vague for now. I'm happy so many others are getting vaccinated first. I am sure my family will eventually have an opportunity to get the shots, and I want to confidently, rather than nervously, roll up my sleeve.
While the mRNA vaccines are new, vaccination is not. There are common safety concerns that usually appear shortly after vaccination and a few other that develop upon exposure to the natural pathogen. There are virtually zero safety concerns that arise long after vaccination.
The trials for both the mRNA vaccines were quite large (10,000s of people). There were no serious side effects reported in both trials. Likewise, the fact that independent trials, utilizing a similar vaccine formulation, found each vaccine to be safe and effective is very reassuring. Of course, larger sample sizes are always better. An additional 7 million people have received the vaccine and there have only been a small handful of easily treatable reactions to the vaccine. Safety concerns with the COV2 vaccines are vanishing with every day.