Dennis W.Macy, DVM, MS; John Chretin, DVM

Veterinary Teaching Hospital, Colorado State University, Fort Collins, USA

Background: An association between the administration of inactivated vaccines (primarily feline leukemia and rabies virus vaccines) and subsequent vaccine site tumor development exists. Inflammation is considered to be a necessary antecedent to tumor production at vaccine sites in cats. All currently available subcutaneously administered rabies vaccines are adjuvanted and produce injection site granulomas. A new nonadjuvanted canarypox rabies vector vaccine has recently been approved for use in cats.

Aims: This study evaluated the injection site reactions of five nonadjuvanted feline vaccine combination products, four of which contained the new canarypox rabies vector fraction in a rodent model that has previously been shown to mimic the local inflammatory response in cats.

Methods: Thirty rats were divided into five groups of six. Each received a sham subcutaneous injection of saline and, on the opposite side, one of five feline vaccine combinations. Group A vaccine contained panleukopenia (P), rhinotracheitis (RH) and calicivirus (C) combination. Group B contained recombinant rabies (RR) with P, and RH fractions. Group C contained RR with P, RH, and C, and a killed nonadjuvanted feline leukemia. Group D contained RR, P, RH, C, Chlamydia (Ch), and a killed nonadjuvanted feline leukemia. Group E contained RR, P, RH, C, and Ch. Twenty-one days postinjection, the skin was tented and the skin fold thickness over the injection sites was measured and tissue was removed for histologic evaluation.

Results: No evidence of granuloma formation was of any of the vaccine groups or saline controls. Histologic evaluation of injections failed to detect any evidence of injection site inflammatory reactions.

Conclusion: If chronic inflammation (granuloma formation) is a necessary antecedent to oncogene activation/tumor suppressor inactivation and subsequent tumor development after vaccination in the cat, these nonadjuvanted nonlocally reactive feline vaccines should be least likely to be associated with injection site sarcoma development.