There was a study long ago which was done with ferrets to see how
CDV progresses in a colony. When the majority of the ferrets were
sufficiently vaccinated, 75 percent vaccinated, very few of the
remaining UNvaccinated ferrets got CDV, but if 75 percent were
UNvaccinated then the disease went through like wildfire. You can
find it in the first edition of the text, Biology and Diseases of
the Ferret, and I suspect that it is also mentioned in the second
edition but lack time to look in them for you,especially tonight.

So, slow spread is a result of the previous vaccinations.

[Posted in FML 7110]