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Dog Behavior Change After Vaccination [Why & How To Respond]

Have you noticed that your dog’s behavior has changed since getting his vaccinations? It’s alarming, right? But is this normal and something us owners should actually expect? And perhaps even more importantly, will your dogs normal and typical behavior return? Well, here’s everything you’ll want to know.

So, why has your dog’s behavior changed after vaccination? Dogs can behave differently after vaccination because their bodies are doing their best to fight off the foreign substances that are in the vaccines. Most dogs are fine within a few hours or days, but some dogs can have long-term reactions due to a negative reaction to the vaccine.

Ultimately, responses can vary because there are so many different variables at play.

The breed of your dog, their age, the vaccine itself, and so on and so forth.

Consequently, only time will tell how your dog bounces back.

But there are certainly things you are going to want to think about, and ways to support your dog through the process.

Keep reading and you’ll be in a much better position than before you landed here today.

Why Has Your Dog’s Behavior Changed Since Vaccination?

Your dog’s behavior could change after a vaccine due to not feeling well, hypersensitivity, an allergic reaction, or inflammation.

Not Feeling Well

As your dog’s body works to fight the tiny amount of disease that has been injected into his body, he may feel slightly unwell.

Most of us behave differently when we are under the weather, and it is the same for dogs.


It could be that your dog is hypersensitive to the vaccine, and his body needs to adapt to the presence of the vaccine so that his antibodies can kick in.

Sometimes the site of the vaccination can become inflamed due to the deposit of immune complexes in the tissues.

Other times, a dog can get vasculitis.

Vasculitis is the umbrella term that describes a variety of skin diseases caused by the small blood vessels of the skin coming into contact with inflammation (see below).

For example, some rabies vaccines can cause local alopecia or dermatitis. You might notice affected patches of skin on the tips of the ears, the tail, scrotum, or footpad.

Vasculitis is most commonly seen in small dogs such as:

  • Terriers
  • Miniature Poodles
  • Bichon Frises
  • Dachshunds

An Allergic Reaction

Your dog could be allergic to something in the vaccine, so you’ll notice changes in his behavior.

For example, some vaccines contain egg protein, so if your dog is allergic to eggs, he is likely to react.

Other components of vaccines that can cause allergic reactions are gelatin or fetal calf serum (these are added to vaccines as stabilizers).

Other times, an antibiotic (such as neomycin) causes an allergic reaction.

Signs of an allergic reaction include:

  • Angioedema (swelling), usually the ears or head
  • Pruritus (itching)
  • Vomiting
  • Acute diarrhea
  • Dyspnea (difficulty breathing)
  • Urticaria (hives), or raised red welts on the skin. These welts are usually on the ears, face, lips, tongue, or throat, though they can occur anywhere on the body

Note: Some of these conditions (such as urticaria) may resolve themselves within 12 to 48 hours, but call your vet urgently to get the correct diagnosis. The above symptoms are similar to those of anaphylactic shock, which can be fatal.

If your dog’s tongue or gums are slightly blue, and he’s having difficulty breathing, this is most likely systemic anaphylaxis: he needs urgent assistance to survive.

Because most of these problems will occur within minutes of exposure to an antigen, keep your dog in the clinic for at least 15 to 25 minutes after he’s received his vaccination.

You want to make sure any immediate problems are dealt with rapidly, particularly if your dog is severely allergic and goes into shock.


Sometimes a dog can change behavior due to inflammation at the injection site.

Slight inflammation is usually no cause for concern and should resolve itself within 12 to 24 hours (or sometimes within 3 days).

Signs that your dog is dealing with inflammation include:

  • Pain at the injection site
  • Lethargy
  • Small behavioral changes
  • Anorexia or significant loss of appetite
  • Coughing or sneezing (with some intranasal vaccines that have Bordetella bronchiseptica. This is a response to the vaccine entering the upper respiratory tract and is usually temporary)
  • Swelling at the injection site (less common, these swellings may be warm to the touch and either firm or swollen with fluid). These swellings can last for up to a week

In rare cases, inflammation as a reaction to a vaccine can provoke early embryonic death in pregnant dogs. You may wish to avoid vaccinating a pregnant dog unless the benefits outweigh the risks at that moment.

Is It Normal For A Dog’s Behavior To Change After Vaccination?

It is normal for your dog’s behavior to change for a few hours or days as he adapts to the impact of receiving the vaccination.

When your dog gets a vaccine, he’s getting a strain of the virus. Your dog’s immune system will then have to learn to fight future invasions.

Most dogs only react slightly to vaccines (see statistics below).

Observe your dog’s behavior, and watch for signs that he isn’t feeling his usual self so that you can offer comfort.

It’s normal for your dog’s body language to change if he isn’t feeling his best after vaccination. You might see:

  • His ears are back or dropped
  • He’s shaking or cowering
  • His lips are pushed forward
  • He’s drooling more than usual

The above signs are normal behavior, but if you spot any of the more severe warning signs of an allergic reaction (see above), call your vet right away as a matter of urgency.

Will Your Dog’s Behavior Return Following Vaccination?

Your dog’s behavior will almost always return to normal eventually. The chances of long-term negative effects are very small.

Most dogs will start behaving normally within a few hours to a few days of vaccination. The risks of long-term impacts of vaccines for dogs are extremely small, according to this study.

Out of 1,226,159 dogs who were vaccinated, the ratio of adverse reactions was 38.2 dogs per 10,000. Most of the reactions (72%) happened on the day the vaccine was given.

65.8% were considered standard vaccine reactions caused by the response of the dogs’ immune systems. 31.7% were allergic reactions, and 1.7% were considered anaphylaxis.

You can see that the odds are very high that your dog’s behavior will return to normal.

Out of the very small percentage of dogs who were adversely affected, the researchers noted that:

  • There is a greater risk of long-term impact of vaccination on small dogs rather than on large dogs
  • Neutered dogs also carry a greater risk of adverse effects
  • Having multiple vaccines in one session also increases the risk of one of them causing a long-term problem
  • The breeds at the greatest risk include Chihuahuas, pugs, Boston Terriers, Miniature Pinschers, and Dachshunds

Make sure your vet isn’t giving the same dose of a vaccine to all dogs irrespective of size. A good vet will consider your dog’s current state of health, his lifestyle, breed, age, weight, and environment.

How To Support Your Dog After Vaccination

To support your dog after vaccination, you’ll want to treat any allergic reactions, request pain relief medicine, or provide relief if he has a fever. Provide your dog the space he needs to rest and recover, and don’t make him eat if he doesn’t want to.

Treat Any Allergic Reactions

If your vet knows your dog is sensitive or allergic to certain substances (or if your vet discovers this after giving the vaccine), your dog will likely receive some antihistamines.

Antihistamines for dogs have different dosages depending upon several factors, but your vet will know what amount is best for your dog.

Some common prescriptions for dogs to help them with post-vaccination reactions include:

  • Meloxicam
  • Benadryl
  • Carprofen
  • Aspirin
  • Deracoxib

The above medications can help with soreness, swelling, and fever.

Note: Be sure to get a prescription from your vet rather than trying to dose your dog yourself.

Request Pain Relief Medicine

Your dog may be in pain after the vaccination – some dogs get sorer than others, but there are ways to find out if your dog is in pain.

Your dog may be in pain if you notice him:

  • Hiding more than usual
  • Not wanting to walk or run
  • Not wanting to eat
  • Not breathing normally
  • Not wanting to be touched or cuddled
  • Whimpering or growling
  • Trying to lick the injection site

If your dog appears to be in severe pain, check with your vet to see if he can be prescribed stronger pain medication.

Provide Relief If He Has A Fever

It’s common for dogs to have a fever as a temporary reaction to vaccination. Use a rectal thermometer to check your dog’s temperature. Here’s how:

  1. Coat the thermometer with a dog-friendly lubricant
  2. Insert it into your dog’s rectum (about one inch deep)
  3. Wait for 30 to 60 seconds before removing it to check the temperature

A normal body temperature for a dog is between 101 to 102.5 degrees F (38.3 to 39.2 degrees C).

If your dog has a temperature above 103 degrees F (39.4 degrees C), then he has a fever.

Note: If your dog’s temperature is around 106 degrees F (41 degrees C), get them to the vet urgently.

If your dog has a mild fever, it will usually go away on its own. However, if you want to make your dog feel more comfortable, you can wipe your dog’s ears or paws with a damp cloth or towel.

Provide The Space He Needs To Recover

Your dog will need extra rest along with peace and quiet. If you have children at home, tell them not to play with or pet the dog for now.

Scratches on the head are fine, or other light touches. Go at your dog’s pace and according to what he wants.

He may not want to eat a full meal, or he may not want to eat much at all. A small treat out of your hand can give him a nice pick-me-up while he’s feeling tired.

Don’t Make Him Eat

Because some dogs lose interest in food after vaccination, some people worry and think they have to get their dogs to eat at all costs.

Appetite loss is a common side effect, but it usually only lasts for about a day or two.

Don’t try to force-feed your dog, as this will only cause stress on top of him feeling unwell.

On the other hand, don’t assume he wants less food either.

Let your dog decide whether he wants to eat or not. He’ll be fine for a day or two without food if he’s still drinking water.

If after 24 hours your dog has eaten nothing (not even a treat), call your vet and see what they think.


It certainly is a cause for concern when our dogs behave differently after vaccination.

In most cases, however, their behavior will return.

How long this takes, and what supportive measures are best for you to implement, will vary from context to context.

This is why liaising with a veterinarian is typically the best course of action.

Rest assured, your dog should be okay in time.

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