What I'm proposing is an intermediate step between doctors and nurses (or perhaps buffing up the powers of higher level nurses so they could operate standalone) so that one doesn't always need to make an appointment with someone with 8 years of specialized training to be stuck with a tetanus booster shot.
We have categories matching that description in the US now, most notably Physician Assistants [0] and Nurse Practitioners [1].
As a patient I don't want this to happen. I'm ok with nurses administering the shot, but by having an MD giving his approval first (or a "Super nurse"). At what point do you draw the line and say "this is enough knowledge, get to work"? What happens when things go wrong? How do you make sure things won't go wrong? It's not like in a lot of technological settings where if the system doesn't boot you can just buy a new one (caricature). You're dealing with the life and quality of life of a human being. Stakes are different.