To dream of injection means receiving a quick solution via the introduction of an input of artificial matter. This quick mode of assimilation can refer to other sources besides the input of chemicals. The indoctrination of propaganda is a kind of injection/ vaccination.
The dream of vaccination refers to taking precaution to defend against a risk. The risk can be a disease, safety violation in a procedure, in driving, or etc.
Dreaming of accepting a jab can mean using a quick solution to meet with a problem. This dream can be a suggestion