Many attempts have been made to develop effective and safe vaccines to protect cats against FIP. Unfortunately most of these studies failed, with ADE observed in several trials. At present there is only one commercial vaccine available (Primucell©, Pfizer). This vaccine is available in the USA and some European countries.
Primucell® contains a temperature sensitive mutant of the type 2 FCoV strain DF2. The vaccine is administered intranasally and aims at inducing local mucosal immune responses through the induction of IgA and cell mediated immunity. However the vaccine also induces seroconversion, although titres are generally low. There is considerable controversy regarding the safety and efficacy of this vaccine. The vaccine contains a type-2 strain, whereas type-1 coronaviruses are more prevalent in the field. Different studies on the efficacy of vaccination in inducing protection against disease have been performed, both under experimental and field conditions.
Although some experimental studies have indicated that vaccination protects against disease, results have not been consistent. Preventable fractions between 0 and 75 % have been reported [Hoskins et al, 1995; McArdle et al, 1995; Scott et al, 1995; Gerber et al 1990]. The results of field studies examining the efficacy of protection have been equally contradictory. No difference in the development of FIP between the vaccinated and placebo group was found when the vaccine was used in Persian breeding colonies [Fehr et al 1995]. In a double-blind trial including 609 cats, no differences between the vaccinated and placebo group were found during the first 150 days after vaccination. However, after 150 days, fewer FIP cases occurred in the vaccinated group compared to the placebo group (1 against 7). In another trial, a preventable fraction of 75% was found when the vaccine was tested in a very large cat shelter in the USA [Postorino Reeves, 1995]. In the latter study all kittens were seronegative prior to vaccination. Therefore it can be concluded that Primucell® might not be effective in seropositive cats that have already been exposed to FCoV. Since Primucell® is licensed for use from 16 weeks of age and is not effective in younger cats [Lutz et al 2002], most kittens (and especially those living in breeding colonies and multiple cat households) have already been infected and are seropositive. This is an important practical limitation for its use. The ADE that was a feature of some experimental vaccine trials has not been observed in field studies, suggesting that the vaccine can be considered safe.
ABCD does not consider the FIP vaccine as a core vaccine. Vaccination can be considered in kittens that are unlikely to have been exposed to FCoV, e.g. from an early weaning programme particularly if they enter an FCoV endemic environment.
If immunization is considered, a primary vaccination course consisting of 2 doses of the vaccine 3 weeks apart from an age of 16 weeks onwards should be given. Vaccination before 16 weeks was not shown to give protection against infection [Lutz et al 2002]. Therefore there are two particular problems in breeding catteries; firstly most kittens are already seropositive at the age of vaccination and secondly FCoV infection occurs much earlier than 16 weeks [Lutz et al, 2002, Addie & Jarrett 1992].
In cats of which the lifestyle has justified primary vaccination, annual boosters may be considered. Although studies on the duration of immunity are lacking, it is thought to be short lived and regular boosters are recommended to maintain immunity.