Randy, the percentage of ferrets we've personally had with true vaccine
reactions is 12% but they were related ferrets.  (The tendency to have
allergies can be more common in some families, as you know.)  Ruffle became
semi-conscious and needed epinephrine; Meltie lost consciousness completely
and had to have epinephrine plus some other meds and oxygen chamber.  Came
within a hair's breadth of losing her.  Both reactions happened rapidly.
One took about 10 minutes and the other was faster, yet.
 
IMPORTANT: it can actually be a GOOD thing if a ferret acts sick --
lethargic, maybe an upset gut -- after a shot.  It means that the immune
system has gone into high gear, which is what a vaccine SHOULD do because
that's how Immunity if built.
 
DO pre-medicate with Benedryl (which also can make them lethargic), and do
worry and get the ferret to vet immediately for anything consistent with
mucus membrane swelling (breathing impairment, badly swollen eyelids, runs
(which may be bloody), swelling, etc), hives, or blood-pressure dropping
(loss of consciousness and so on).
 
It's a scary situation; sometimes a heart-breaking one, but the illnesses
being prevented are also heart-breaking, and while many, many ferrets have
the normal sickness-like response of the immune system going into high gear
like it should or a bit of a bump left at the injection site, few seem to
have actual reactions.  This is also what happens when humans get vaccines;
we adults don't have to do that often but it's expected when we do.  We get
a bit grumpy, a bit sore, and feel like we're coming down with something --
our bodies are being tricked into thinking we are sick so that we will
develop antibodies to the illness and fight it off as soon as we are
exposed.
 
Everyone should try to remember: ASK YOUR VET WHAT TO EXPECT IN TERMS OF
NORMAL RESPONSES TO VACCINES AND WHAT TO CONSIDER A POSSIBLE DANGEROUS
REACTION.  (Do it with your physician when a vaccine is given, too.)
[Posted in FML issue 2369]