Antibody responses to inactivated (adjuvanted) and attenuated (non-adjuvanted) feline panleukopaenia virus vaccination, including in different injection sites.

ObjectivesVaccines have traditionally been administered to cats into the interscapular subcutaneous region ('scruff') for ease of restraining the cat while the vaccine is injected. Concern about feline injection-site sarcomas (FISSs) has prompted recommendations to use distal sites such as the hindlimb or tail, but evidence of adequate immune response at these sites is limited. This field study evaluated the antibody response to feline panleukopaenia virus (FPV) in kittens vaccinated with one of two commercial vaccines, injected at different sites.MethodsAn inactivated (killed), adjuvanted pentavalent vaccine (Fel-O-Vax 5; Boehringer Ingelheim Animal Health Australia) was injected subcutaneously into the scruff, left distal hindlimb or proximal tail. A modified-live virus (attenuated [MLV]), non-adjuvanted trivalent vaccine (Feligen RCP; Virbac Animal Health Australia) was given into the scruff only. For the latter, an inactivated, adjuvanted monovalent feline leukaemia virus vaccine was administered concurrently into the contralateral scruff, left distal hindlimb or proximal tail. Only one FPV-containing vaccine was administered to each cat/kitten: either the inactivated vaccine given in one of the three different anatomical regions or the MLV vaccine given into the scruff only. Cats were re-vaccinated in the same site and using the same vaccine type. Kittens were randomly allocated into study groups according to order of recruitment. Kittens were sampled at four time points over 12 months (T0, T1, T2 and T12). Protective FPV antibody titres were determined by haemagglutination inhibition (HI; negative <1:32, positive ⩾1:32).ResultsSamples from 100 kittens (T0, T1, T2) and 77 returning adult cats (T12) were available for FPV antibody testing (median age of kittens at T0 was 13 weeks, range 7-16). Eight kittens (8%) were found to be HI-positive at T0. Protective titres did not differ significantly among the three injection sites for the inactivated vaccine. Linear modelling demonstrated that antibody titres were higher in kittens given the MLV vaccine compared with kittens given the inactivated vaccine at T1 (P = 0.006) and T12 (P = 0.001). However, the proportion of kittens protected in each group (MLV vaccine vs inactivated vaccine) was the same. For most kittens (91%), a single vaccination was sufficient to produce protective antibody levels, irrespective of whether they were given the MLV (scruff) or inactivated vaccine (at any site). Age and sex had no effect on antibody titres after vaccination. Two kittens (2%) failed to achieve protective titres after two doses of vaccine and required re-vaccination between 16 and 18 weeks. Inexplicably, one (1%) adult cat lacked a protective antibody titre response at T12 despite earlier seroconversion.Conclusions and relevanceBoth inactivated and MLV vaccines induce protective titres against FPV. Although most kittens aged above 7 weeks are protected 1 month after a single vaccination, some require re-vaccination to develop protection. Some kittens require a final vaccination at 16 weeks or older and a booster 6-12 months later to develop robust protective titres. Comparable FPV antibody responses are elicited when inactivated vaccines are administered into the scruff, left distal hindlimb or proximal tail. Notably in this study, the MLV vaccine tended to produce higher antibody titres. These results support evidence-based recommendations on vaccination site selection to mitigate FISS risk in jurisdictions where this condition is prevalent.