Current vaccination recommendations from an immunologist's viewpoint (Proceedings)

Recent recommendations for vaccination of dogs and cats have diverged from the previously adhered to yearly multiple booster schedule. New improved vaccines and vaccine strategies coupled with studies that demonstrate that duration of immunity is indeed longer than was previously believed, have made it possible to immunize most adult dogs and cats on a three year schedule. When we fully understand the nature of the immune response it is reasonable to assume that induction of immunological memory by an initial series of vaccines, followed inevitably by "self- boosting" during environmental exposure will ensure that an animal is protected for at least several years.

The process of vaccination in a naïve animal first expands pools of T lymphocytes then induces expansion and maturation of clones of B lymphocytes that react specifically with the pathogen present in the vaccine. These activated B cells develop into both plasma cells making specific antibody and memory B cells that are capable of responding even more rapidly the next time the antigen is encountered. If the vaccine antigen is presented in a form that replicates (as a modified live virus or one of the new viral vectored vaccines) then not only are T helper cells activated, but there are also T effector/cytotoxic cell clones expanded. These cells are capable of killing virus infected cells to limit the infection and viral replication. In the older animal the presence of memory T and B cells makes the response to antigen (either virulent or vaccine) more robust and more rapid.

The downside of too frequent vaccination is that the continual polyclonal stimulation in some dogs may lead to increased development of autoantibodies and subsequent autoimmune disease. The other unpleasant side effect is the potential to development allergic reactivity to the vaccine. In either case the patient becomes sick from a procedure meant to provide protection from disease. With feline patients an added concern exists for development of vaccine induced fibrosarcoma. Increased incidences of such adverse responses to repeated vaccination has been one of the factors stimulating the change in vaccination frequency.

In this talk I will discuss

• the AVMA vaccine guidelines for dogs and cats

• duration of immunity studies that exist

• expected immune responses from different vaccines

• adverse vaccine reactions

• the immunological basis for current recommendations

• relevance and usefulness of titer determination