Vaccination of cats also has risks

In the past, most veterinarians, like most physicians, believed that vaccination was an entirely safe procedure. We knew that the administration of effective vaccines prevented disease, but we did not suspect that they could actually cause disease as well. Veterinarians learned over a period of time, however, that some of the available vaccines are capable of causing reactions as immediate and severe as anaphylactic shock, as intermediate as injection-site reactions, and as long-term as the delayed development of cancers related to the vaccine components themselves.

The cat seems to have a highly reactive immune system. It is one of the only species in which we see eosinophils, white blood cells that participate in the inflammatory process, normally circulating in the bloodstream. Although routine annual vaccination of cats for many different diseases has been considered a prudent preventive measure for decades, we know now that this is not necessarily so. A few years ago, veterinarians started noticing that a particular type of very deadly cancer known as fibrosarcoma would start growing at the site of vaccination injections in some cats. It took several years for the veterinarians who first noticed this association between vaccine injection sites and the site of fibrosarcoma development to convince their colleagues and the vaccine manufacturers that this association was real and an important source of cancer for cats. Finally, thorough studies showed that, in fact, multiple repeated vaccination injections could lead to the development of cancer in some cats.

Vaccine manufacturers continued these studies to try to understand what factors in these vaccines were most important. Some studies suggested that the FeLV and rabies vaccines were most responsible for causing fibrosarcoma, but other studies suggested that a larger number of products could lead to disease as well. Some studies seemed to show that adjuvants, “immune-booster” substances added to certain types of vaccines, were the problem, but experts are not unanimous in agreement about this. Because of all of this research, the American Association of Feline Practitioners developed recommendations for the vaccination of cats to minimize the risk of not only the most serious vaccine-associated complication, fibrosarcoma, but also lesser complications.

All veterinarians should be following these guidelines when recommending a vaccination program for their feline patients. All cat and kitten owners must have a thoughtful discussion with the veterinarian of their particular pets’ risk factors before vaccines are administered. Not all kittens and cats should receive all vaccines every year. As a matter of fact, most cats should not be vaccinated yearly at all, especially after the kitten series and the first few annual boosters. Some experts argue that the actual risk of vaccine-associated reactions is small in a large population of cats. Although this may be true, it is equally true that the risk of contracting many diseases is even smaller for some cats that is the risk of serious vaccine reactions, especially for cats kept indoors. It is this comparison of one kind of risk versus another kind of risk that is important to the decision to vaccinate for a particular disease or not. All kittens and cats deserve this thoughtful analysis and deserve for this analysis to be repeated regularly as risk factors change throughout a cat’s life.

Certainly, vaccination against infectious diseases will continue to be an important part of health maintenance for all cats. The single most important thing kitten owners can do for the health of their youngsters, however, is to commit to an indoor life for their pets. Keeping one’s cats indoors alone or as part of a stable group of healthy felines will do more to ensure that every individual enjoys nine long, healthy lives than any other measure possibly could.