EVALUATION OF THE SAFETY AND EFFICACY OF A MODIFIED-LIVE FIPV VACCINEUNDER FIELD CONDITIONS

The safety and efficacy of a modified live FIPV vaccine was evaluated in a double-blind placebo controlled field study. Two high risk popula tions for FIP were vaccinated either with a placebo or the vaccine. Th e clinical outcome was monitored for at least 12 months after vaccinat ion. In the first population of 138 purebred cats from catteries with a history of FIP losses, the vaccine was found to be safe but without overall efficacy. In the second population, consisting of 609 domestic and purebred household pet cats, no protection against FIP was observ ed during the first 150 days after vaccination (FIP cases: vaccine n = 12, placebo n = 10); however, there were significantly less FIP death s in vaccinates (n = 1/238) compared to nonvaccinates (n = 7/256) in t he period from 150 days post-immunization onward. Vaccination did not have any apparent side effects and there was no evidence for antibody dependent enhancement of FIP. Fifty to 95% of the cats in the respecti ve household pet and purebred cattery populations had FCoV antibody ti ters of 1.25 or higher at the time of vaccination, indicating prior ex posure. Retrospectively plasma taken at the time of first vaccination was also found to be positive for FCoV RNA by polymerase chain reactio n in some of the cats which died later of FIP. Prior FCoV exposure may have accounted for the apparent vaccine failure, especially among pur ebred cattery cats.