Well, Cornell concluded from the above that vaccine efficacy in a
laboratory setting is highly dependent on the challenge. It offers
protection at low challenge doses, none at higher doses. The problem is,
no one
knows what the “real world” dose level is.

Another problem is that there are actually two strains of FIPV. Just as
there are many different flu strains or cold strains which cause you to
get sick several different times with the flu or a cold, because each
time you catch a different strain for which you aren’t already immune.
Type I strain of FIP is believed to be the most prevalent in the “real
world” but it is the most difficult to reproduce in a laboratory. Type
II is easier to reproduce, but not as prevalent outside. It is not
known how effective a vaccine against one type will be against the
other type.

So, while some of the studies have found the current vaccine effective
against the Type II strain of FIP, there is no evidence either way as
to if it will work against the Type I strain.