Vaccinations save lives and are an important part of keeping dogs safe and healthy. By vaccinating early and regularly, serious and even fatal infectious diseases, like canine parvovirus and rabies, can be avoided entirely. While the benefits of vaccinations greatly outweigh the risks, vaccine reactions in dogs are possible and do happen. Here’s everything dog owners need to know about dog vaccine reactions.
Do Dogs Develop Vaccine Reactions?
Modern vaccines are extremely safe and effective, but dogs can still experience vaccine reactions. In almost all cases, dog vaccine reactions are mild and do not require treatment, but in very rare cases, more severe reactions can occur and require immediate medical intervention.
In 2021, a study published by the National Institute of Health evaluated 1,226,159 dogs receiving 3,439,576 vaccine doses. Out of all these dogs and vaccines, only 4,678 vaccine reactions were recorded. This equates to 38.2 reactions per 10,000 dogs, or in other words, only 0.00382 percent.  Additionally, the majority of these dog vaccine reactions were mild and self-limiting, such as soreness and lethargy.
Small breed dogs have a higher risk for vaccine reactions. As a dog’s size increases, the risk of an adverse vaccine reaction decreases. Studies have also shown that neutered dogs have a slightly higher chance of having an adverse vaccine event . Lastly, the more vaccines that are administered at one time, the higher the risk of an allergic reaction.
Dogs with immune-mediated diseases are not at a higher risk for vaccination reactions despite a popular theory that vaccination could induce a relapse of that disease. Fortunately, research does not support a link between vaccination and the development of immune-mediated diseases.
Most Common Vaccines That Cause Reactions
The highest rate of vaccination reactions in dogs occurs after the Lyme disease vaccination.  This may be due to the size of Borrelia burgdorferi, the bacteria that causes Lyme disease, or one of the ingredients used to help induce an appropriate immune response. Reactions after the Lyme vaccine are most often limited to local pain at the injection site and resolve without intervention.
Historically, the leptospirosis vaccination triggered a higher rate of dog vaccination reactions. This was due to both the size of the bacteria and the bovine serum used to increase the efficacy of the vaccinations. In response to the higher rate of reactions to the vaccine, the original formulation was withdrawn and revised. Today’s leptospirosis vaccine utilizes only a portion of the main bacteria, and in a recent study of over 1 million dogs, the leptospirosis vaccine was not found to be more likely to cause a reaction when compared to other vaccines. 
Types of Vaccine Reactions in Dogs
Most vaccine reactions in dogs are systemic, meaning that the whole body is affected. This could be general malaise after a vaccination, a mild allergic reaction, or a more severe allergic reaction known as anaphylaxis. Systemic vaccination reactions in dogs can also be delayed, in which case the reaction happens 24-48 hours after the vaccine was administered. Delayed vaccine reactions are exceedingly rare.
Localized vaccine reactions are also possible. These types of reactions only affect the animal where the vaccine was given. Usually, the local reaction is soreness or mild swelling, both of which resolve in a few days. Some dogs, however, will form small, firm bumps under the skin where the vaccine was given. For these, veterinarians use the 3-2-1 rule. The bump is not a concern unless it persists for three months after an injection, becomes larger than 2 centimeters in diameter, or continues to increase in size one month after an injection.
Signs of Dog Vaccine Reactions
After a vaccine is injected, it will stimulate an inflammatory response. This ensures that the body recognizes the antigen, triggers the immune system, and creates the antibodies needed for protection. Therefore, mild inflammatory symptoms after vaccinations are expected and common. Dogs with mild, common vaccination reactions can display one or more of the following:
- Soreness or swelling at the injection site
- Mild fever
- Reduced energy
- Decreased appetite
- Sneezing after a nasal vaccine
These symptoms are all considered part of the normal vaccination process and are a sign that the body is working toward creating the protective response. Pet parents should take note of these and keep a close eye on their dog for resolution of the symptoms, but treatment is not usually necessary, and no modifications need to be made for future vaccinations.
Signs of serious vaccine reactions in dogs are as follows:
- Vomiting or diarrhea
- Puffy eyes
- Swollen muzzle
- Small, raised bumps on the body
- Difficulty breathing
These symptoms can indicate anaphylaxis, a severe and exaggerated immune response to the vaccine. Anaphylaxis can be life-threatening without treatment. If a dog displays any of these symptoms, you should seek veterinary care right away. Typically, anaphylaxis occurs within the first hour after the vaccine was given, but it can occur up to 24 hours later.
Treating Vaccine Reactions in Dogs
If a dog is having a serious vaccine reaction, immediate treatment is necessary. Fortunately, veterinarians can effectively treat vaccine reactions in dogs. The sooner a veterinarian is able to intervene, the easier it will be to stop the inflammatory cascade driving the allergic reaction.
In most cases, dog vaccine reactions are treated with a combination of injectable antihistamines and steroids. Signs usually resolve shortly after a veterinarian administers these medications.
More severe vaccine reactions in dogs may require hospitalization for intravenous medications, fluid therapy, and monitoring.
Vaccine Reactions in Dogs: Things to Keep in Mind
Recently, exaggerations of potential adverse effects have discouraged dog owners from having their canine companions vaccinated. This is mostly due to the development of the internet and social media, which allow people to spread their opinions and re-share data out of context. Much of the hesitancy regarding vaccines is the result of the negative effects and lower efficacy of the earliest vaccines, in spite of the fact that these issues have been resolved.
Vaccinations have saved more lives than any other medical intervention, and while dog owners should be aware of possible vaccine reactions, they should take comfort in knowing that canine vaccinations are safe and effective, dog vaccine reactions are very rare, and veterinarians are well equipped to treat serious adverse events if they do occur.
- Tizard IR. “Adverse consequences of vaccination.” Vaccines for Veterinarians. 2021:115–130.e1. doi: 10.1016/B978-0-323-68299-2.00019-8. Epub 2020 Jul 10. PMCID: PMC7348619. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7348619/#:~:text=Out%20of%201%2C226%2C159%20dogs%20receiving,%25%20were%20considered%20%E2%80%9Cvaccine%20reactions%E2%80%9D
- Moore GE, Guptill LF, Ward MP, Glickman NW, Faunt KK, Lewis HB, Glickman LT. “Adverse events diagnosed within three days of vaccine administration in dogs.” J Am Vet Med Assoc. 2005 Oct 1;227(7):1102-8. doi: 10.2460/javma.2005.227.1102. PMID: 16220670. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/16220670/
- Brooks, Wendy. “Vaccine allergic reactions in dogs and cats.” Veterinary Information Network. Retrieved from: https://www.vin.com/vetzinsight/default.aspx?pid=756&catId=102903&id=4951409&ind=808&objTypeID=1007