As with any medical procedure, there is a small chance that reactions may develop as a result of vaccination. Your pet may experience discomfort at the injections site. Mild fever. Decreased appetite or energy. Development of a small, firm, non-painful swelling under the skin at the injection site. Sometimes an allergic reaction may occur. Swelling of face or muzzle. If an allergic reaction occurs give our office a call… we may ask you to come back in so the Doctor can assess the situation and/ or administer a antihistamine.