IMRAB 3 is the right vaccine but it has NOT been tested for being longer
lasting than a year in ferrets, so *no one* knows how long it does last
in them beyond a year.  As a result it is an annual vax in them.  There
can be a LOT of variation across species lines in how long vax last and
titer levels are *not* firmly known.  Here is the info you need, complete
with time factor in the chart:
http://www.avma.org/pubhlth/rabcont.asp
[Posted in FML issue 4644]