It happens. Rarely, but it happens.
I never saw one in my years of practice, or my lifetime of working with cattle - until I lost a calf about 3 year ago, to what I'm fairly certain was anaphylactic reaction to a Clostridial bacterin. Of course, at the time, we turned 'em right out of the chute and into the pasture - and she went over the top of a little rise and was dead and stiff before we realized something was amiss, because her dam kept running back and forth bawling for her. Even if I'd had epi on hand(which I didn't) I wouldn't have know she was having a reaction.
So...now I keep some epi close by when we're vaccinating, and kick the vaccinates into a holding pen so that I can sort of keep an eye on 'em 'til we finish working the herd. At least that way, if one was having some trouble, I'd have a chance to attempt saving 'em.