[user104658]

Depends, its a bit more complicated than that really. The process of giving an injection (at least into the muscle, so you don't have to find a vein) isn't that difficult - although you do have to make sure it ISN'T in a vein as A) it'll be ineffective and B) you'll cause bleeding and heavy bruising.

Dosage won't be an issue either as they'll be packaged as individual doses, most likely.

However what might be an issue - especially with Pfizer - is that some of these vaccines are li'l snowflakes and need to be handled properly or they won't work as effectively (i.e. Some won't work at all). They won't harm you, but they also won't immunise you. However that's fairly easily solved by having a few experienced staff in charge of handling and distribution, and the less experienced staff just doing the stabbin'.