[Broken_Hippo]

I know some folks have reactions to vaccines: not everyone does, though. And weirdly, when folks don't know, sometimes the placebo gives them reaction. Pretty much, side effects have to happen more often in the real thing than they do a placebo.

Sometimes it just doesn't work to have double blind: LSD trials, for example, make things pretty obvious. It isn't the case for the flue, though.

You are correct on the trials: most folks don't get called. That said, living outside the city doesn't exclude you from trials in general because they generally need participants with x and/or y. Often, they will pay for expenses to travel, especially if your disease is uncommon or they have trouble finding participants.