These transmissible vaccines will likely first be used in animals(that you eat of course) that carry diseases that can infect people. Some may use a weakened version of the virus, or attach a piece of the pathogen to a benign virus. Other treatments are aimed at people who are already infected and will prey on the virus dwelling in their cells.
It’s early days for these kinds of vaccines and therapies, and scientists still have to show that they are effective and safe to use in wildlife or people.
There’s already at least one vaccine known to be contagious, although it wasn’t intentionally designed that way.
At all costs they are trying to reach the entire population with vaccines for complete and total world domination.
Source article was from PopSci http://www.popsci.com/contagious-vaccine-virus#page-2