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Dog Behavior Changes After Vaccination

Vaccinating your dog is crucial to protect them from various diseases. Although the benefits of vaccination are great, some dogs may react to the shots. In this blog post, our veterinarians in Denver will discuss the most common reactions to dog vaccines and what actions to take if your dog experiences any behavior change.

Why should I get my dog vaccinated?

Ensuring that your dog receives its vaccinations during the early years of its life and regularly as an adult is crucial for it to have a long, healthy life. Three illnesses that can be fatal, particularly in young puppies, are rabies, hepatitis, and parvovirus, which can be very costly for pet owners.

Vaccinating your dog against these diseases is recommended rather than treating them after they have already developed. The risk of your dog having a severe reaction to a vaccine is generally very low, and, in the majority of cases, this risk is well worth the benefits of vaccination."

Does my dog need all the available vaccines?

Your veterinarian will assess the risk factors affecting your dog based on its breed, age, and lifestyle and then recommend the appropriate vaccinations.

What are the most common reactions to vaccines in dogs?

It is always possible for adverse reactions to occur during medical procedures, including vaccinations. As a pet owner, watching your beloved pet respond to vaccinations can be upsetting, but it's essential to remember that most reactions are mild and temporary. If you are aware of the symptoms of a reaction and know what to do if your dog exhibits them, it can make receiving vaccinations less stressful for both you and your pet.


Dogs generally feel lethargic and uncomfortable after receiving their vaccinations, and their mild fever is also frequently present. The word "off" comes to mind when most describe this feeling. Your dog's immune system is functioning well and is appropriately reacting to the vaccine in this reaction. It should only take a day or two for these minor symptoms to pass. Contact your veterinarian if your dog doesn't feel better within a few days.

Lumps & Bumps

Lumps and bumps are common reactions to dog vaccinations, just like feeling 'off.' Following the vaccination, a small, firm bump may form where the needle was injected into the skin or muscle, leaving the area tender. These bumps form as a result of your dog's immune system rushing to resolve the localized irritation.

Sneezing & Cold-Like Symptoms

While most vaccines are administered via injection, the Bordetella bronchiseptica and parainfluenza virus vaccines are administered via drops or sprays into the dog's nose. Reactions to these vaccines can resemble a cold, with coughing, sneezing, and a runny nose. Most dogs recover from these symptoms within a day or two. If your dog develops more severe symptoms or does not recover within a few days, it is time to consult a veterinarian.

Serious Reactions To Vaccinations

While most dog vaccine reactions are mild and short-lived, our canine companions can have more severe reactions that require immediate medical attention in rare cases.

Anaphylaxis—This severe allergic reaction can involve facial swelling, diarrhea, itchiness, hives, vomiting, and breathing difficulties. It usually occurs very soon after your pet receives the injection (typically while you are still at the vet's office) but can happen up to 48 hours after the vaccine is given.

Shock - The symptoms of shock following vaccines can include a slow heart rate, decreased blood pressure, and generalized weakness. You may also see a gray tongue and pale mucous membranes.

Can I prevent my dog from reacting? 

Vaccines are an essential way to protect the overall health of your furry friend, and the probability of them experiencing a severe reaction to a vaccine is quite low. However, if your dog has had an adverse reaction to a vaccine in the past, it is crucial to inform your veterinarian. Your vet may recommend avoiding a specific vaccine in the future.

Administering multiple vaccinations simultaneously slightly increases the risk of adverse reactions, especially among smaller dogs. To reduce the likelihood of such a reaction, your veterinarian may advise breaking up your dog's vaccinations over several days instead of all at once.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

To learn more about vaccinations and preventive healthcare for your dog, contact our Denver vets today to book an appointment.

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