There was a non-painful way in development years ago. It was a small patch with micro needles on it all very short, and they sat on the skin for a day. The patch would slowly inject through those little needles the medicine or vaccine. I do not know what happened to this idea.
One can always snort a vaccine, but those are usually LIVE vaccines or partly active anyway, and that is not my idea of fun.
Sadly, laws of science often dictate that we do what we do, because it works, not because it is easy.
So far as I know there is no way to get into outer space except a huge powerful rocket. Costs money, loud, big, etc... why can't we levitate?
Science doesn't allow it.
I think the oldest known vaccine was a cow-pox vaccine. People who milked cows could get cow-pox and were lightly ill, but were then immune to the deadly small-pox (and that is still the case today!). The cow pox pustule was popped on a sick cow using a thorn or needle. The thorn/needle was actually partly hollow, so it took up some of the cow-pox virus. This thing was then jabbed into a persons skin. The cow-pox was close enough to the small-pox virus in terms of its outer protein structure that the body learned from the cow-pox and was ready for the more deadly small-pox. I believe this was discovered by Pasteur.
So see this poking the skin thing is as old as time. Think of it as an ancient initiation ritual. Like a tattoo or piercing.
What grinds my gears is that I am losing my ability to see the computer screen well enough to do my job, and there are no computer chairs that don't hurt my butt.