I only know personally of one accidental injection.
Grade two student, epi-pen was kept in a backpack hanging at front of crass with big sign that it had <student name's> epi-pen. A trouble-making kid (really, he was just a major trouble maker) took it out of the back pack, was playing with it at recess and jabbed himself in the fleshy part below the thumb.
(School decided epi-pens were to dangerous and would now be kept locked in the office. I helped the mom change their mind. It switched to student carrying it himself.)
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It did prevent a school secretary from accidentally self injecting. She was trying to show someone how she knew all about epi-pens and how to use them. From across the room I said "that's not a trainer" and she said "yes, see, it said generic". She held it, ready to swing and jab. And I said louder "it has a needle and epinephrine". I went over and showed her there was an expired date. Then I dug through the drawer and took out the trainer and showed her the difference.
I then suggested the trainer not be kept with the real epi's. What if a trainer was grabbed in an emergency?