Vaccine Reactions in Dogs and CatsVaccine reactions can range from mild to severe in both dogs and cats. The immune system can have a variety of responses to vaccines, and some allergic reactions will develop within an hour and others can be delayed and last for days. Continue reading to learn more about vaccine reactions, symptoms that may develop, treatment, and what to do to reduce future reactions.Are you concerned about your pet?Book a video consultation with an experienced veterinarian within minutes. Rating: 4.9 - more than 1600 reviewsRating: 4.9 - more than 1300 reviewsRating: 4.9 - more than 1600 reviews Download app Symptoms of Mild Vaccine Reactions in PetsSymptoms of mild vaccine reactions can last for a few hours to a couple of days. The most common symptoms include:LethargySoreness at the injection siteReduced appetiteMild fever (normal temperature for dogs and cats is about 102F, a mild fever would be below 103.5F)Treatment, if any is even needed, typically includes a short course of a non-steroidal anti-inflammatory prescribed by your vet. Do not use over-the-counter medications, including aspirin, unless your vet specifically tells you to.Symptoms of Severe Vaccine Reactions in PetsSevere vaccine reactions can start to develop within 30 minutes of receiving a vaccine. Symptoms include:Hives or welts on the bodySwelling of the face, around the eyes, and muzzleVomitingDiarrheaDifficulty breathingPale gumsRapid heart rateCollapseIf your pet develops any of these symptoms, be sure to let your vet know immediately. If your regular clinic is closed, call the emergency clinic and start driving over there as soon as possible.Treatment for Vaccine Reactions in Dogs and CatsTreatment of vaccine reactions typically consists of injections of a steroid, an antihistamine, and possibly epinephrine if the reaction is really severe. Your pet will likely be safest remaining at the vet clinic for 8 to 12 hours to see if additional doses of treatment are needed and to be sure veterinary care is immediately available if the reaction worsens.An IV catheter may need to be placed and IV fluids started to support the cardiovascular system. Once your pet is ready to leave the vet clinic, they will likely go home with an oral steroid and antihistamine to continue for the next few days to deter additional delayed reactions.Should my pet be vaccinated if they’ve reacted in the past?If your pet had a vaccine reaction in the past, be sure to let your vet know before getting any future vaccines. Pets that had reactions such as hives or mild swelling to the face can likely be vaccinated again in the future.Your vet will likely recommend giving your dog or cat pre-medication injections of a steroid and antihistamine 30 minutes prior to being vaccinated. Ideally, they should be left at the clinic for 8 hours to monitor for reactions. This means it’s best to get the vaccines done in the morning on a day your vet clinic is open for a full day. It’s also ideal to only give one vaccine at a time and separate vaccine doses by 3 weeks if your pet has had a reaction in the past.If your pet had a life-threatening vaccine reaction in the past, such as collapse, severe facial swelling or difficulty breathing, it would be safest to never vaccinate your pet again with the vaccine that caused the reaction. If your pet is given that same vaccine again, it could be deadly.Will my pet have reactions to every vaccine?It’s important to know that just because your pet reacted to one vaccine does not mean they’ll have reactions to other vaccines. For example, if your dog had a reaction to the Leptospirosis vaccine, they can still get their Rabies, Distemper/Parvo, and Bordetella vaccines. If your pet received multiple vaccines on the same day and you’re are unsure which vaccine caused the reaction, discuss pre-medications before future vaccines and splitting the vaccine doses apart by 3 weeks to see how your pet responds.Read more:What You Need to Know About Vaccinating Your DogWhat You Need to Know About Vaccinating Your CatNeed to speak with a veterinarian regarding vaccine reactions in your pet or another condition?Click here to schedule a video consult to speak to one of our vets. You can also download the FirstVet app from the Apple App Store and Google Play Stores.