Which animals should not be vaccinated?

Every dog and cat should be appropriately immunised, and each individual animal should be vaccinated as frequently as considered necessary by their veterinarian to provide protection. The vaccination protocol to be followed and the vaccines to be used should be determined within a veterinarian–client–patient relationship. The decision should be determined by factors such as the individual animal’s health status, the animal’s age and likely effects of maternally derived antibodies (MDA), the particular disease and environmental risks to the animal, and the duration of immunity (DOI) of available vaccines.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).