Comparison of the safety and efficacy of a recombinant feline leukemia virus (FeLV) vaccine delivered transdermally and an inactivated FeLV vaccine delivered subcutaneously.

The efficacy of a new recombinant FeLV vaccine (rFeLV), delivered transdermally via a needle-free delivery device was compared to that of an inactivated FeLV vaccine (FeLV-k), administered subcutaneously, with a conventional needle and syringe. Kittens were immunized with either rFeLV (0.25 ml, transdermal) or FeLV-k (1 ml, subcutaneous); or they were sham-vaccinated with physiologic saline (0.25 ml, transdermal). Two vaccinations were administered 21 days apart. Injection sites were monitored for any acute or subacute reactions relative to vaccine administration. Four weeks following the final vaccination, all cats were subject to oro-nasal FeLV challenge. Blood was collected for determination of FeLV antigenemia (p27) at weekly intervals beginning three weeks post-challenge. All of the vaccinated cats from both groups resisted FeLV challenge; and 90% of the control cats developed persistent FeLV antigenemia in response to challenge. No acute or persistent injection site reactions were observed. The rFeLV, delivered transdermally, provides protection against persistent FeLV antigenemia following a robust challenge that is equivalent to that of FeLV-k.