Dog Behavior Changes After Vaccination

Vaccinating your dog is important, as the benefits usually outweigh the risks of reactions to the vaccines. However, some dogs can react to getting their shots. Our Novato vets have provided information on the most common reactions to vaccines in dogs and guidance on what to do if your furry friend has a reaction.

Why should I get my dog vaccinated?

Ensuring your dog receives its vaccinations early in life and regularly as an adult is crucial for its long and healthy life. Diseases like rabies, hepatitis, and parvovirus can be very dangerous for your pet and even fatal, particularly in puppies. It is always better to prevent these illnesses by vaccinating your dog than to treat them after they have already developed. The risk of your pet having a severe reaction to a vaccine is generally low, and in most cases, the benefits of vaccination outweigh the risks.

Does my dog need all the available vaccines?

Your veterinarian will assess the potential risks for your dog based on its breed, age, and lifestyle. After that, they will provide you with advice on which vaccinations are appropriate for your dog.

What are the most common reactions to vaccines in dogs?

Adverse reactions are always a possibility with medical procedures, including vaccinations. It's understandable for pet owners to feel concerned when their beloved pets show any reaction to vaccinations. However, it's important to keep in mind that the majority of the reactions are mild and transient. Being aware of the symptoms of a reaction and knowing what to do if your dog exhibits them can make the vaccination process less stressful for you and your dog.


After receiving their vaccinations, dogs may feel tired and uncomfortable. They may also experience a mild fever, making them feel "off." However, this is a normal reaction, as their immune system responds appropriately to the vaccine. Generally, these symptoms should only last for a day or two. If your dog still feels unwell after a few days, it is recommended that you contact your veterinarian for further advice.

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 reactions to dog vaccines are mild and short-lived, in rare cases, our canine companions can experience severe reactions that require immediate medical attention.

Anaphylaxis - This severe allergic reaction can involve facial swelling, diarrhea, itchiness, hives, vomiting, and breathing difficulties. This type of severe reaction 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.

Why do behavior changes happen in dogs?

If you notice any unusual behavior in your dog after they receive their rabies shot or other vaccinations, there could be various reasons behind it. It's crucial to take these factors into account when assessing your dog's reaction to the vaccines they have received recently:

Individual Sensitivity - Just like humans, dogs have different sensitivities and reactions to vaccines. Some dogs may be more susceptible to experiencing behavioral changes, while others may show no noticeable difference.

Vaccine Components - Vaccines contain specific components, such as adjuvants or preservatives, to enhance their effectiveness and shelf life. In rare cases, dogs may exhibit allergic reactions to these components, leading to more pronounced behavioral changes. Discuss any concerns with your veterinarian to ensure the right vaccines are administered.

Stress and Anxiety - Veterinary visits, including vaccinations, can induce stress and anxiety in dogs. The anticipation of discomfort, strange environments, or unfamiliar people can trigger temporary changes in behavior. Comforting your dog with gentle reassurance and positive reinforcement can help alleviate stress during these visits.

Can I prevent my dog from reacting? 

It is essential to vaccinate your dog to ensure their long-term health. The risk of a serious reaction to vaccines is very low, but if your dog has had a previous reaction, you should inform your veterinarian. They may advise you to skip a particular vaccine in the future.

When administering multiple vaccinations at once, there is a slight increase in the risk of adverse reactions. Smaller dogs may be more susceptible to this.

To minimize the risk of adverse reactions, your veterinarian might suggest spacing out your dog's vaccinations over a few days instead of giving them 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 Novato vets today to book an appointment.