Dog Behavior Change After Vaccination – How to Handle a Vaccine Reaction


For most dogs, the benefits of following the appropriate vaccination schedule at the correct times will significantly outweigh any potential risks. That said, some dogs experience some minor side effects and will display various behavioral changes.

Vaccine reactions can be stressful for dog owners, but that does not necessarily mean they should be treated as a significant concern. By learning about some of the most common vaccine reactions in dogs, you will be better prepared to help your pooch.

How Can We Help?

This informative guide will explain some of the most common reactions and more unusual side effects of dog vaccines for things like kennel cough, Lyme disease, distemper, and the rabies virus. From there, we will explain what you can do to help your dog through any potential reactions or adverse side effects.

Table of Contents

Common Vaccine Reactions and Post-Vaccine Behavioral Changes

While most dogs will not experience adverse effects after a vet-recommended vaccination, some will exhibit behavior changes. Mostly, these reactions will be mild and will not last more than a few days. 

Even though most reactions are nothing to be overly concerned about, it can still be helpful to know what types of reactions are common. It can also help to know what types of reactions can occur, as it will help you feel less stressed the next time your canine companion needs a new vaccine.

Chronic Sneezing and Sniffling

While most vaccines are administered to dogs via injection, vets can give certain types in the form of nose drops or sprays. While these vaccines can be just as effective as those injected, they can result in various cold-like symptoms.

These types of vaccines, also known as intranasal vaccines, were developed to help prevent respiratory viruses and diseases, like Bordetella Bronchiseptica Virus and Parainfluenza. An intranasal vaccine is more accessible to administer to a struggling dog than a sharp needle.

While these vaccines are effective, they can result in various post-vaccination symptoms, like repeated sneezing, sniffling, coughing, and a runny nose. Most dogs will recover from these symptoms after a few days, but it can be worth reaching out to your veterinarian if the dog’s symptoms do not improve after the third day.



Lethargy and a general lack of enthusiasm are the most common behavior changes a dog will display after receiving a vaccine. This is because some vaccines will give a dog a mild fever. 

Fevers are a perfectly normal reaction to a vaccine and prove that the vaccine is working and the dog’s immune system is actively responding to the vaccine. In addition to lethargy, your dog may seem like they are in discomfort.

Fortunately, these symptoms are perfectly normal and should last only a day or two. If the dog appears extremely lazy and will not even eat their food or react to otherwise exciting stimuli, like treats and walks, you may want to speak with your veterinarian. The same is true if the dog’s lethargy continues for more than 48 hours.

Your veterinarian may prescribe some form of pain relief or anti-nausea medication to help your dog cope with the vaccine-related symptoms as they recover their strength.

Hypersensitivity and Inflammation Near the Injection Site

In some cases, a dog’s behavioral changes following a vaccine can be related to physical pain. As the dog’s body reacts to the presence of the vaccine in the bloodstream, inflammation can occur. 

Inflammation can make the skin feel hypersensitive. You may also notice lumps and inflammation of the tissue surrounding the injection site. If your dog is experiencing physical pain, it may react by being distant. They might also recoil if you touch them.

Smaller dogs are more prone to these specific symptoms, so you should not be overly alarmed if your small or toy breed dog seems to be in physical discomfort following a vaccine.

Again, this is nothing to be overly concerned about; however, it can become an issue if it does not resolve itself after a few days. The lumps and bumps near the injection site should also disappear over one or two weeks.

If the inflammation is still present two weeks after the dog was vaccinated and they still seem sensitive and distant, you should book an appointment with your veterinarian. 

What Are Some Less Common Vaccine Reactions, and When Should You Be Concerned?


While the above-mentioned vaccine responses are relatively common and should not be viewed as a primary concern if they resolve themselves after a few days, some physical symptoms and behavioral changes are very concerning.

The following are not common responses to a vaccine, but they can occur:


This term refers to an allergic reaction to a vaccine, which can quickly become life-threatening if not addressed appropriately. Typically, it will occur very soon after administering the vaccine (usually within minutes or hours).

In most cases, the dog will develop hives, facial swelling, and diarrhea, and they will vomit and struggle to breathe. If you notice these symptoms, return your dog to the veterinarian immediately, as it can be dangerous.

If your veterinarian is unavailable, contact an emergency clinic immediately.

Read the MSPCA Guide to Anaphylaxis in Dogs and Cats for more information about anaphylaxis in dogs.

Severe Pain and Visual Signs of Infection

While it will not occur as quickly as anaphylaxis, another rare but severe reaction to a vaccine can be physical pain triggered by an infection.

When the dog received their injected vaccine, the needle may have been contaminated with bacteria, or bacteria entered the injection wound through other means. A severe infection can occur when bacteria penetrate the tissue beneath the outer skin.

The infection can be excruciating for the dog, which can trigger a wide range of changes in behavior. You may also notice visual signs of infection, including discolored skin, discharge around the injection site, and swelling. The dog may also recoil if you attempt to touch the area near where they received their vaccine.

If you notice physical symptoms or behavioral changes, take your dog back to the veterinarian as soon as possible.

How Can You Help Your Dog Avoid Negative Vaccine Reactions?

Although many of the vaccine reactions mentioned above are natural and should not be seen as a significant concern, there are ways you can reduce the chances that your dog will experience them.

For starters, spread out the vaccines your dog receives over multiple appointments. Research backs the claim that dogs will experience fewer reactions if they receive a single vaccine rather than multiple vaccines in a single sitting.

While making multiple trips to the veterinary clinic can be more time-consuming and expensive, it can help your dog experience fewer mild symptoms, like lethargy.

You can also help your dog avoid experiencing severe symptoms by ensuring they receive all of their vaccines appropriately. Many vaccines are given while dogs are still in their puppy life stage. While they can be given to adult dogs that did not follow the vaccination schedule as puppies, the chances that the animal will experience side effects can increase with age.

You should also ensure your veterinarian has access to the most up-to-date vaccination rate possible. This is particularly important if you have recently moved to a new clinic, state, or country. Suppose your dog had an adverse reaction to a particular vaccine in the past. In that case, you should explain this to your veterinarian, as they may have alternative options available for your pooch.

How Should I Handle My Dog’s Vaccine Reactions?

Since most vaccine reactions are entirely normal and relatively mild, you do not have to do much to help your pooch recover. For the most part, keeping an eye on your pet’s symptoms to make sure they recover on time and that the symptoms do not worsen is the best thing you can do.

You can also offer your dog food that will be easier on their stomach than their regular kibbles. Some dogs do well with baked, unseasoned chicken breast and white rice. Simply shred the chicken and mix it in with the rice.

Try to avoid loud noises and give your pet space. Imagine if you were recovering from a cold and try to treat your dog with the same respect.

Most importantly, report any changes in the severity of your dog’s symptoms to your veterinarian.

For More Information

If you want to know more, PetMD has an informative article titled Vaccine Reactions in Dogs – Side Effects and What You Should Know.

You can also read the Guilford – Jamestown Veterinary Hospital’s guide How to Handle a Vaccine Reaction in Your Dog.

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