Vaccinations are generally safe, but pets can experience mild side effects, such as localized swelling or discomfort at the injection site, lethargy, or a slight decrease in appetite. Serious adverse reactions are rare but can occur. Serious reactions include, but are not limited to: hives, vomiting, diarrhea, difficulty breathing, facial swelling and potentially collapse. If you notice any concerning or severe reactions, promptly contact your veterinarian, or seek emergency veterinary care after hours.