They told me that after the 2nd shot it was 'for life'. However... when I got the 2nd shot that changed.... don't remember the spread they told me but it was big.... something like anywhere from 3 to 10+ years.

The only shot I can remember actually 'hurting' was a pneumonia shot I got some years ago... no side effects but the 'soreness', (unless you call that a side effect), was severe and lasted over a week. I could barely raise my arm. As far as soreness the worst ever was:

Army, Basic Training. We got I think 11 shots over two days. Drill Sergeants loved to make you go thru the horizontal bars the day after you got the shots knowing the excruciating pain it would cause.