leukemia vaccination has only be shown to be efficacious for kittens. Any vaccination of non kitten adult cats should provide the client with written informed consent information that vaccination would be at best investigational medical care. One should not vaccinate adult cats for leukemia without written client information that cats develop an age resistance to FELV disease. The pet vaccine industry and vets should fess up and tell the public leukemia vaccine efficacy trials of adult cats failed because the unvaccinated challenge cats could not be made sick without immuniosupressive drugs. Every time a cat is vaccinated for leukemia the chance of sarcoma cancer increases.
see
http://evidencebasedvet.com/forum/viewt ... 8b4b835e60