Actually, some vets don't know how to give the injection properly!!! or at least they can't be bothered.
I took all six of mine to a vets closer to home for their myxi last year, and it was given all under the skin. When I questioned the nurse who had been present she tried to make an excuse and said it was a new brand of vaccine and that's how it was given now. Obviously when I came home I did some research and I was lied to. I complained and sent them a copy of the data sheet for the vaccine. I got a letter from the vet stating that she did give part intradermally and trying to suck up to me, but I know for a fact that she didn't, I was holding my bunnies at the time and none was given intradermally, it was straight in and out!
It does still offer immunity, just not as much as it would had it been given properly.