I'm no physician or medical expert, my field of study was physics not medicine so I defer to the medical experts but I can read and comprehend things scientific and from what I've read on the respiratory system, it seems to me that a great deal of the body's immune response mechanism is concentrated in the mouth and nose where most everything is being taken into the body. I'm guessing that the mucous membranes of the nose, mouth and lungs are going to produce things like histamine a lot quicker than the skin. Is it not true that some things that you may breathe in or swallow may be harmless but devastating if you got them in a cut or puncture of your skin? I'm just assuming that the immune system has more resources concentrated around openings in the body even though our marvelous immune systems go after invaders no matter where they are. I have an idea that breathing in a vaccine may be less likely to make me ill than an injection. Every time I've ever received a flu shot, I have become very ill. ^_^
TDD