And the lollipop
As a child, the best (and the only) good part about going to the doctor is the lollipop we get after the examination. It makes the visit to the doctor that much more sufferable and worth our while, and in many cases, these lollipops are the only bargaining card parents have when taking their children to see the doctor.
However, as grownups, we don’t care as much about the too-sweet candy, and doctors know that. What could they use, then, to get grownups to go to the doctor and get vaccinated? Oh yeah, that other thing, the part about not getting sick. If that isn’t incentive enough for adults to visit the doctor, I don’t know what is.