I note that many people are concerned that mRNA vaccine technology has never before been approved for use in humans. They worry about unknown risks and nasty surprises, and are reluctant to accept the Pfizer and Moderna vaccines.
I am actually not worried about it, and I'll try to explain why. First I'll just note that this technology has been under development for decades, and has been tested extensively in animal models and experimentally in humans before the large-scale clinical trials that have led to Emergency Use Authorization. So there is a lot of evidence for safety, although it is true that the follow-up time for the clinical trials is so far less than is usually required for full approval. The trial subjects are still being followed so we will get a signal if anything untoward might happen -- but there is very good reason to be confident that it won't.
This is pretty technical, and it's hard for people who haven't studied a lot of biology to get this stuff sometimes, but I'll do my best. Many readers will already know this, others may not. In animal cells (also plant cells, actually) the DNA in the nucleus, that kind that's in our chromosomes, contains instructions for making proteins. In simple terms, one gene consists of the instructions to make one protein. Proteins are long chains of smaller molecules called amino acids. The instructions consist of three unit combinations of four different "letters," which are also specific small molecules, and you probably know these are abbreviated A, T, C, and G.* So AAT might mean one amino acid and GTC another. But these instructions need to be translated by a mechanism for assembling proteins.
The instructions are carried out by molecular machines in the cell called ribosomes. Messenger RNA, mRNA, is the molecule that carries the instructions from the nuclear DNA to the ribosomes. There are regulatory regions in DNA that mark where a gene begins and ends (some genes consist of separated regions whose instructions need to be spliced together, not important) and for turning on and off reading of a gene by mRNA. Fortunately we don't have to worry about any of this because the mRNA vaccines skip all that.
Here's what they do instead. Cells are wrapped in a membrane that has little portals that selectively let molecules in and out, called receptors. Viruses consist of genetic material inside a protein capsule, with little keys that unlock one of the receptors so the virus can get its genetic material into the cell. The immune system learns to recognize one or more of the proteins in the viral capsule and make antibodies that attack that protein. In the case of these particular mRNA vaccines, that protein happens to be the key that gets the virus into the cell, which is often the case.
Note that the protein by itself is completely harmless. It's only dangerous when it's part of the virus; it can't reproduce on its own, and it doesn't hurt anything if it binds to a receptor if it's not associated with any viral genes to inject. So the vaccine manufacturer makes a whole lot of mRNA that consists of the instruction to make the viral protein. They make it a little bit different in some ways from natural mRNA, so it won't provoke an immune response itself, is more stable, and can sneak into cells. That part is very technical but don't worry about it. You can read all about it here if you're interested.
So you get injected with this and some of your cells take it up and start making the viral protein. They display it on their surfaces, your immune system recognizes it and starts making antibodies. Then the cell destroys the mRNA as it does all mRNA in the normal course of events -- it's job is done. So there is really no evident way that you could suffer any long-term ill effects from this.
Now, because the vaccine provokes such a strong immune response you may briefly experience typical symptoms of a viral infection. That's because those symptoms are actually caused by the immune response, not the virus itself. You don't have a viral infection, so the symptoms will go away quickly. I'm talking a fever, or feeling fatigue, or a headache. From what we've seen of the clinical trial data, something like 20% of people might have this experience, but it sure beats suffocating alone.
So when you have the chance, that's the information you should consider. By then, we'll have at least a couple more months of follow up anyway. So I'm not worried. This technology has all sorts of incredible potential, not only against viruses but also against cancer and maybe some other applications. Once you have the basic platform, you can plug in any protein you want, very easily. These are the days of miracles and wonder.
*Not that it matters but these stand for adenine, thymine, cytosine and guanine.