What makes you think the labor shortage has anything to do with the vaccine mandate? A few months ago, some were blaming the labor shortage on the extended unemployment benefits (which were really pretty pitiful to begin with and wouldn't be enough to keep me from getting a job.) Now, those benefits have been gone for at least a month and there's still a labor shortage. On the other hand, we've heard form some people posting here that they've applied for work at Amtrak, and it seems to take the company forever to get people on board, even after they've made a job offer and it's been accepted. Maybe the problem is more the fact that the hiring process is arcane and inefficient.
Just because some random OBS tells you that a few of his or her colleagues are quitting rather than get a pretty low-risk vaccine really means nothing. After all, the plural of "anecdote" is not "data."
I seriously doubt that the Amtrak labor shortage (or any labor shortage) is a result of the vaccine mandate. Seems more like anti-vaxxer disinformation to me.