Efficacy of a canarypox virus-vectored vaccine against feline leukaemia

New canarypox virus-feline leukaemia vaccine found to be effective

source: H. Poulet et al
Veterinary Record vol 153 no 5, August 2 2003
starts p141, 5 pages long

Feline Leukaemia virus (FeLV) causes significant illness and deaths among domestic cats world wide, and there is a need for more effective vaccines, as well as more evidence of the efficacy of FeLV vaccines. Live virus vaccines give rise to a broader immune response than inactivated virus vaccines, but there are safety concerns relating to live attenuated FeLV vaccines. Live viral vectors offer an alternative. The canarypox virus vector (ALVAC) offers possibilities because it multiplies in birds, not mammals, but is able to give mammals a protective immune response by expressing foreign immunogens.

This study used a canarypox-vectored live vaccine to give protection against FeLV. The vaccine was tested on FeLV-free and seronegative kittens aged between seven and nine-weeks-old. The vaccine was found to be effective against very severe challenges, and was solid twelve months following the initial vaccination.

Most diseases relating to FeLV are suffered by cats with persistent FeLV infections, so it is important that a vaccine can prevent such infections. Cats may, however, suffer latent infections, with the virus hosted in their bone marrow. This latent infection may become active when cats are given corticosteroids. There was no latent infection detected for most of the cats given the ALVAC-FeLV vaccine.The vaccine appears to have induced a broad enough immunity to lower infections with FeLV to levels at which they could not be detected.

The vaccine also proved efficacious with no adjuvant. This helped to achieve local tolerance, and there was no inflammation when samples from the site of the injection were examined. The vaccine has an advantage in not provoking reactions, since it is possible that chronic inflammation at sites of injections could be linked to fibrosarcomas in vaccinated cats. The vaccine is also compatible with other vaccines. The article examines methods and results of this study in further detail.