Mild-Moderate Adverse Vaccine Reactions in Dogs and Cats
Vaccination involves the intentional stimulation of your pet’s immune system, and unintended consequences infrequently occur. It is not uncommon for your pet to feel “under the weather”, with reduced energy and/or appetite for 12-48 hours following vaccination.
Dogs will occasionally develop facial swelling/scratching, hives, and/or nausea within 24 hours following vaccination. These signs are usually self-limiting, but resolve much faster if treated by your veterinarian as early as possible with injections (shots) of steroids and antihistamines. Vomiting may occur in conjunction with these signs, or with the more severe signs discussed below.
Severe Adverse Vaccine Reactions in Dogs and Cats
Severe, life-threatening reactions are rare, though any change in breathing rate, sounds, or effort, as well as incoordination, collapse, repeated vomiting, or other concerning signs should be evaluated by a veterinarian immediately. If they occur, these signs are analogous to a human with a severe bee sting allergy, and almost invariably arise within minutes after vaccination. Also very rarely, stimulating the immune system by vaccination can cause a delayed immunity to the body’s own blood cells (termed Immune-Mediate Hemolytic Anemia, or IMHA), which can become life-threatening. Weakness, lethargy, collapse, or altered mental state hours, days or weeks after vaccination would be indicative signs.
Less than one in ten thousand cats may develop a swelling at the injection site that goes on to become cancerous (“injection site sarcoma”) and requires surgical removal. These have become much less common in recent years due to reformulation of vaccine mixtures and more careful vaccination scheduling. Additionally, feline vaccinations are now typically administered over the limbs rather than the neck to help identify which vaccine caused the problem as well as to aid surgical planning if it becomes necessary.
Medical Response to Adverse Vaccine Reactions in Dogs and Cats
The leptospirosa vaccine in dogs has historically been associated with more frequent adverse reactions than other vaccines. For that reason, it is important that you discuss your pet’s lifestyle and risk of developing the disease with your veterinarian. Very rarely, some dogs have developed kennel cough after receiving the vaccine.
If your pet develops a reaction, depending on the type, you may consider altering your pet’s vaccination schedule in consultation with your veterinarian. It may become necessary to have your pet monitored by a veterinarian for several hours following vaccination or to pre-treat with medication that lessens the risk/severity of reaction without blocking the effectiveness of vaccination.
Again, the above adverse reactions are uncommon, and have been judged by international veterinary panels after rigorous debate and scientific study as being a smaller risk than not vaccinating in most cases. Discuss your pet’s specific needs with your veterinarian.
The following links provide additional information about vaccination recommendations and risks.