In veterinary medicine, non-core vaccines are vaccines which could be considered optional, depending on the animal, the animal's lifestyle, and where the animal lives. This is in contrast with core vaccines, vaccines which are strongly recommended and sometimes even required by law. Generally, your veterinarian will evaluate your animal's individual case to determine which non-core vaccines are suitable, and he or she will discuss your options with you when offering vaccinations.
Vaccines can be classified as non-core for a variety of reasons. For example, some animals don't go outside, which means that they are exposed to far fewer diseases, and this would make vaccination for those diseases rather superfluous. Other animals board a lot, coming into contact with animals which may have conditions such as kennel cough, making vaccination against these diseases important for well-being. In other cases, vaccines are classified as non-core because the benefits of the vaccination do not outweigh the risks in the case of most animals.
As a general rule, veterinarians rely on guidelines issued by government agencies and professional associations to determine which vaccines are core, and which are non-core. These guidelines are different for different species, obviously, and they may include complicated sidebars which discuss specific situations in which non-core vaccines might be considered core vaccines. When assembling these guidelines, officials think about the incidence of a particular disease in a region, and the known risks of vaccinating for it.
When your animal is vaccinated, the vet may have a brief interview with you to determine which non-core vaccines should be recommended. If your animal is indoor-only, this will reduce the number of vaccine recommendations, while indoor-outdoor animals or working animals may require more vaccines. Certain vaccines may also be recommended in the event of travel; for example, if you take your horse to a region where the West Nile Virus is present, you should vaccinate for it before traveling.
When discussing non-core vaccines with your vet, be sure to ask about the potential risks of the vaccines, and ask for his or her honest opinion about whether or not your pet needs them. While it can be tempting to vaccinate for everything imaginable, this is often not necessary, and it could even be potentially harmful. If your pet does receive non-core vaccines, make sure that they are noted in the immunization record, especially if your pet boards, because this information may be needed at some point.