1) Go get vaccinated. Please.
2) Side effect for me on Moderna Shot #1 was a sore arm days 2 and 3, and a little fatigue. Side effect on shot #2 was a sore arm on days 2 and 3, and that was it. Other people have felt flu-like for a day or so, usually after the second one, if they never had COVID before.
3) Good luck to your son, he'll be fine, nothing to it.