Antibody responses to feline leukaemia vaccination: exploring the effect of sex, boosting schedule, site of administration and vaccine type.

ObjectivesHistorically, vaccines have been administered in the dorsal interscapular region of cats (the 'scruff' of the neck) owing to easy access to the subcutaneous space. In response to concerns about sarcomas developing at injection sites (feline injection site sarcomas [FISSs]), and a possible association between feline leukaemia virus (FeLV) vaccination and the development of FISS, alternative FeLV vaccination sites such as the distal left hindlimb and tail have been proposed by influential vaccination bodies and various key opinion leaders. There is a dearth of evidence, however, to demonstrate the development of a comparable immune response after FeLV vaccination in these sites.MethodsThis field study was undertaken to investigate the FeLV anti-surface unit (SU) antibody response in FeLV-uninfected cats inoculated with one of three different FeLV vaccines (Fel-O-Vax 5, Fel-O-Vax Lv-K or Leucogen FeLV), administered in one of three different anatomical locations ('scruff', left distal hindlimb or tail). Kittens were sampled at three different time points, 1 month apart (T0, T1, T2) and again 12 months later (T12). Testing with a published anti-SU ELISA to detect FeLV-A and FeLV-B antibody responses to vaccination was performed. Antigen p27 testing, PCR testing to detect FeLV proviral DNA and neutralising antibody (NAb) testing to identify any FeLV-infected or FeLV-exposed animals were also performed.ResultsA total of 125 kittens were recruited and allocated into one of nine vaccine groups, with 105 kittens completing the initial course of vaccinations and blood draws, and 83 cats returning for T12 sampling. No progressive or regressive FeLV infections were detected in the entire kitten or adult cohorts. A total of 14 (11%) kittens and two (2%) adults tested FeLV NAb-positive. Females had higher (approximately 1.6-fold) post-vaccinal FeLV-A and FeLV-B antibody concentrations compared with males (P = 0.003 and 0.009, respectively). An anamnestic response ('booster' effect) was observed, with FeLV-A and FeLV-B antibody levels higher at T2 (day 56) after two primary vaccine doses than at T1 (day 28) after one dose (P = 0.004 and P <0.001, respectively). No biologically significant differences in FeLV antibody concentrations were found between the different sites of vaccination or vaccine formulations. Tail injections produced fewer vaccine 'non-responders' against FeLV-A at T2 than scruff and hindlimb vaccination (P = 0.020), possibly because tail injections were actually intramuscular, due to a lack of subcutaneous space in the tail.Conclusions and relevanceFeLV vaccines can be administered in the scruff, left hindlimb or tail of cats, with comparable antibody responses observed across all sites. This result will assist veterinarians in making evidence-based recommendations about possible sites for FeLV vaccinations.