system
Given the following post, respond as if you're commenting on Reddit:
human
How are vaccines delivered via needle?

I've gotten a number of vaccines through my life, most recently the Covid one and it got me thinking.

-why aren't vax shots done in the veins and arteries? Why the arm muscle? If it's in the vein, wouldn't that carry the "product" around faster?

-is the muscle and everything just mass covered with veins so that chances are the needles hit the veins anyways? 

-why are vaxes via needles and not tablets like antibiotics? 

-if the vax/needle is put in the arm/muscle, how does that product move around the body? Does our immune system just update our OS with the new info and its filed away?

-why the arm soreness? Is it because a needle pierced the muscle? If so, wouldn't that pain happen right away like stubbing a toe? Or does the arm hurt from the product? And why?

Hope these questions actually made sense! And thanks in advance!

Edit: I'm seeing very helpful answers below, thanks to everyone who answered. Other than replying to you all individually, to each comment to say thanks, I don't know how to "like" or "heart" a reply here, or whatever the reddit equivalent is lol. If I have more questions I'll post or reply to the answers.
gpt
They're meant to remain in place for more than a few hours to better stimulate an immune response. Most vaccines have an adjuvant - something to help it stick around longer and further stimulate the immune system, like an oil or protein-based antigen.

Some vaccines are oral (rotavirus, poliovirus), others can be intranasal (some flu vaccines) or even intradermal (I believe the mpox vaccine was given intradermal to get more vaccinations from a single vial).

E: to expand

1) Probably not a good idea to give most vaccines in a vessel. Some are modified live and best kept locally. There are some places you may not want them to go directly. That's why the vaccinator will often pull back on the syringe - to make sure it's not in a vessel.



2) The adjuvant can help keep it around, but most of it is cleared within ~48hrs.



3) Your arm is sore because of the immune response happening there - white blood cells coming in and breaking up the vaccine components and updating the OS as you say. Sometimes, your local lymph nodes may be sore, too (ie in the armpit), because the white blood cells have migrated there to update the OS more centrally.