It's supposed to be an intramuscular shot, and you've got muscles all over. It would be surprising if there was a serious reason they could not administer it in the buttock or thigh (unless, of course, you're getting it through a car window at a big vaccination site). As long as the person giving the shot is experienced at giving IM shots, it seems like you could get it in a different location than the upper arm. On the other hand, I wouldn't let this concern stop me from getting the shot. If they insist in the arm, I'm taking it in the arm.
Most of the shots are being given in public settings, so I don't think the buttocks or thigh is really going to be a realistic option if you get the vaccine now. If you wait, which means you have to keep isolating and such a lot more than when you get vaccinated, there will be more vaccine available in doctor's offices in which case it will be private and you can get it wherever you want. I got my first shot at a community center, and there wasn't going to be any drop trou, if you get my drift. However, I will say, I got the Moderna, and the arm did hurt a fair amount for about 3 days and then it was just gone. But I wouldn't really want to have that kind of pain either in my thigh or my buttocks, as they're harder to avoid putting pressure on than the arm muscle. But again, if you wait long enough, it will be up to you, but right now, it's not.
I don't know what "arm reactions" you've had, or what that means, but like Pax, I got the Moderna shot, and the arm pain is REAL. I can't imagine having that in my thigh or butt.
Mine lasted 2.5 days. I woke up on the third morning, and it was just gone.
I was told (by the pharmacist that gave mine) they could only give the shots in the LEFT arm, but wasn't given a reason for that. Everyone I've talked to that's had the shots has had them in the left arm. Can't imagine what the reason could possibly be...
I had the Moderna vaccine and like others who had it, my arm was really sore, swollen and red. After a couple of days it got itchy, but after about the third day, it was fine. I also had a lot of fatigue. I always have them do flu shots in my right arm and because I'm right handed, that arm is stronger than my left. Although a flu shot swells up and gets sore, it doesn't last as long as the shot(s) in my left arm.
Paxiled: I know they say you get the worst side effects from the second Moderna shot, but I had very little with the second one. A little fatigue and the arm soreness was about it. It doesn't seem like soreness even lasted as long as it did with the first shot.