Immunization

• Active immunization can partially or completely protect dogs and cats from severe consequences of infection with a variety of different pathogens, and in some cases it reduces shedding of these pathogens. • Vaccines contain attenuated live microorganisms, inactivated microorganisms, or portions of these organisms. They also contain preservatives and adjuvants. • Failure of immunization can occur with improper storage or administration of vaccines, a large challenge dose, host factors such as concurrent infections or disease, and interference by maternal antibody. • Other adverse effects of vaccine administration are uncommon to rare but include hypersensitivity reactions, disease induced by live attenuated vaccine organisms, and injection-site sarcomas in cats. • The decision to administer a vaccine should be based on discussion of risks and benefits between the veterinarian and pet owner. This should be documented in the medical record. • Guidelines for vaccine selection and administration have been published by a number of veterinary bodies, such as the AAFP, AAHA, AVMA, and WSAVA; suggestions can also be found in Appendix I.