The bigger concern at this point is how many people will willingly take the shot. It is beginning to appear that many plan to wait until they see how the early takers do.
Most people in need won't hesitate. And we have limited shots in the beginning, so not having a huge demand first is a good thing. Then once it is more proven by literally millions the rest can sign up.
Employers can also force the hesitants later on. Death too.