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 injection 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.