https://www.youtube.com/watch?v=O6cfvdG5FU8Just swallow a tablet containing dead viral cells, and get up to 10 months immunity. It's difficult to see what side effects there could be. It's also very cheap to produce. Will it become available?
Overall, the form of administration doesn't really matter unless there is a problem of bioavailability or stomach damage. Your muscles have rich blood supply and when you inject medicine, it gets absorbed quickly. Side effects totally depend on the medicine itself, doesn't matter whether it's tablet or not.
By the way, to my mind, it's not a good idea to increase your immunity by taking some meds once a year. That way you are making your body lazy and incapable on its own in future.
