Hazards Associated With Vaccines

In addition to the antigen, vaccine suspensions also contain other ingredients which may include other antigens, protein from tissue culture or egg yolk, preservatives like antibiotics, and carrier proteins such as aluminum for enhanced immunogenicity. Therefore, adverse reactions may result as a response to the antigen or to anyone of these additional components. Over the years, improvements in techniques for antigen development and better purification procedures for the production of vaccines has resulted in fewer hazards associated with immunization. However, adverse reactions may still occur in certain individuals. The following are some potential hazards associated with vaccination:

Immunosuppression

Canine vaccines immunizing against several infectious diseases are routinely manufactured as pre-mixed for administration as all-in-one-vaccines; that is, one inoculant contains many different antigens that are administered as a single "shot". Such vaccines are termed polyvalent vaccines as opposed to monovalent vaccines, which would contain only antigen directed at immunizing against a single infectious agent.

Concerns have often arisen regarding the widespread use of polyvalent vaccines because they are believed to cause a significant decrease in immune function known as immunosuppression. Immunosuppression may result when the amount of antigen introduced into the dog exceeds the ability of the immune system to respond. Such a condition is termed antigen-overload. Immunosuppression may also occur as a result of one antigen component of the vaccine preventing the immune system from responding to another antigen component of the polyvalent vaccine. This latter form of immunosuppression is termed vaccine interference.

Clinical studies exploring different polyvalent vaccines have demonstrated a significant degree of immunosuppression associated with inoculation with polyvalent vaccines; however, duration of immunosuppression was only 7-10 days. Therefore, from a clinical standpoint, such a brief period of immunosuppression in an otherwise healthy dog is not considered cause for concern. However, if a nutritional deficiency or hereditary immune disorder already compromises a dog's immune system, the added immunsuppression may result in clinical illness if the dog is exposed to an infectious disease within the 7-10 day margin. Alternatively, if the dog has already been exposed to an infectious disease and is in the process of defending against a mild infection which is asymptomatic, the increase in immunosuppression caused by administration of the polyvalent vaccine may also result in clinical illness. In the latter situation, clinical symptoms of infection will present within 24-48 hours following vaccination. In these situations, it is common for many dog owners to blame the vaccine for causing the disease, when in actuality, the vaccine only made the underlying condition apparent. In light of this, in dogs suspected of harboring mild infections or who may be immunosuppressed due to other factors (immune disorders, seasonal allergies, certain medications), vaccination with polyvalent vaccines should be postponed until the underlying condition has resolved, or if risk for contracting infectious disease is high, use of monovalent vaccines or killed vaccines might be an alternative option.