Pet vaccination is increasing in number and frequency, and as a result, illness after vaccination has been on the rise in sensitive dogs and cats. Unfortunately, most traditional veterinarians are not adequately trained to recognize acute and chronic vaccination reactions in pets. Typical vaccine reactions may range from immediately after vaccination to days, months, or even years later. Symptoms occasionally seen in the first 24 hours of vaccination include fever, tenderness, facial swelling, hives, swollen lymph nodes, vomiting, diarrhea, and rarely, acute liver and kidney failure.
Transient or chronic seizure disorders may also develop in sensitive pets that have had vaccines. Immune suppression that may last for up to seven days can also occur after vaccination. Some of the chronic disorders suspected of being the result of overvaccination include lupus, pemphigus, rheumatoid arthritis, and autoimmune platelet and red blood cell disorders. Chronic skin and ear allergies, as well as food allergies and inflammatory bowel disease may also be triggered by vaccine reactions. The immune response of dogs with preexisting inhalant allergies (atopy) to pollens has shown to be augmented by vaccination. The autoimmune diseases Hyperthyroidism (cats) and hypothyroidism (dogs) have often demonstrated in humans to be initiated by vaccinations, and this is also suspected in dogs and cats. In susceptible cats, refractory injection site fibrosarcomas (aggressive, malignant cancers) may appear months to years after receiving a feline leukemia or rabies vaccination.