The Most Controversial Dog Vaccines. Which Ones Cause the Most Reactions?


Vaccinating dogs is crucial to protecting them against dangerous and often fatal diseases like rabies, parvovirus, distemper, and more. However, like any medical treatment, vaccines do carry potential risks and side effects. While serious adverse reactions are very rare, some dogs may experience milder reactions like lethargy, fever, pain or swelling at the injection site. Understanding which vaccines tend to cause more frequent reactions can help pet owners make informed decisions when developing a vaccination schedule with their veterinarian. This overview examines common canine vaccines, reasons for reactions, and steps to minimize risks while still protecting your dog’s health.

Vaccinating dogs safely is key to reducing the spread of infectious diseases that threaten both animal and human health. Studies show high rates of morbidity and mortality associated with canine rabies, especially in regions with large populations of free-roaming dogs and low vaccination coverage ( Responsible dog ownership includes staying up-to-date on core vaccines recommended by veterinarians based on the dog’s lifestyle and risk factors. However, being aware of potential vaccine reactions empowers owners to make choices that minimize risks while still protecting their pets.

Most Common Vaccines for Dogs

There are core and non-core vaccines recommended for dogs. Core vaccines are considered vital to all dogs based on risk of exposure, severity of disease or transmissibility to humans. According to the American Animal Hospital Association (AAHA), the core vaccines for dogs are:

  • Rabies – Rabies is fatal once clinical signs develop, and vaccination is required by law in most jurisdictions. Rabies vaccines are considered core for all dogs. (Source:
  • Distemper – Canine distemper virus (CDV) causes fever, cough, vomiting, diarrhea, seizures, and sometimes death in dogs. It is highly contagious and vaccination is considered core.
  • Parvovirus – Canine parvovirus causes severe vomiting and diarrhea in puppies and dogs. It is extremely contagious and can be fatal. Vaccination is considered a core part of puppy and adult dog protocols.
  • Adenovirus – Canine adenovirus (CAV-1 and CAV-2) causes infectious canine hepatitis, which affects the liver, kidneys, spleen, lungs, and blood vessels. Vaccination is core.

How Vaccines Trigger Immune Response

Vaccines work by activating the immune system to recognize a pathogen as foreign and mount a response against it without causing disease. When a vaccine containing antigens is injected, the immune system identifies the antigens as foreign invaders and produces antibodies specifically designed to target them. Antibodies, along with other immune cells like T cells and B cells, work together to destroy the target antigen, creating immunological memory. If the real pathogen enters the body in the future, the immune system is primed and ready to stop infection before it can take hold and cause disease [1]. Vaccines essentially train the immune system by exposing it to a weakened, partial, or inactivated form of an antigen so that it can mount a quick and robust response when encountering that antigen again [2]. Rather than developing immunity through becoming sick, vaccines allow us to develop immunity through a controlled activation of the immune system without the detrimental effects of natural infection [3]. These mechanisms prepare the body to ward off disease much more effectively than if it faced the pathogen with a naive immune system.

veterinarian giving dog vaccine injection

Potential Vaccine Reactions

Vaccine reactions in dogs can range from mild to severe. Mild reactions are relatively common and may include soreness, swelling, or redness at the injection site that resolves within a few days. Lethargy, mild fever, and decreased appetite are also potential mild vaccine reactions. More significant reactions like hives, facial swelling, or vomiting are less common but can occur within hours after vaccination.

Some dogs may experience severe, life-threatening reactions including anaphylaxis, a dangerous whole-body allergic response. Anaphylaxis causes sudden vomiting, diarrhea, shock, seizures, and death in extreme cases. Though rare, anaphylaxis is an acute emergency requiring immediate veterinary care (Dog Vaccine Side Effects and Adverse Reactions). Other severe reactions like autoimmune diseases are poorly understood but may develop over weeks or months after vaccination.

While most reactions are minor, it’s important to monitor dogs closely after vaccinations and contact a vet immediately if severe symptoms appear. Preventing reactions involves screening for risk factors and taking precautions like separating vaccine components.

Most Reactogenic Vaccines

Some vaccines tend to cause more reactions than others in dogs. According to experts, the most reactogenic vaccines include:


The rabies vaccine is known to commonly cause reactions in dogs. Rabies vaccines contain inactivated virus that triggers a strong immune response. This can sometimes lead to reactions like facial swelling, hives, lethargy, and fever. However, the rabies vaccine is extremely important for protecting dogs against this fatal viral disease [1].


Leptospirosis vaccines protect against bacterial infections that can damage the kidneys and liver. Older versions of this vaccine were associated with more reactions, but modern leptospirosis vaccines have become less reactive over time. Still, mild reactions like lethargy and decreased appetite may occur [2].

Lyme Disease

The Lyme vaccine defends against Borrelia burgdorferi bacteria transmitted by ticks. Some dogs experience lethargy, fever, and soreness at the injection site after receiving this vaccine. However, the Lyme vaccine is important for dogs in areas where the disease is prevalent.

Mechanisms of Vaccine Reactions

Vaccine reactions are caused by a dog’s immune system responding to the ingredients and adjuvants in a vaccine. While vaccines help develop immunity by activating the immune system, sometimes the response is more severe than intended.

Some key mechanisms behind vaccine reactions include:

  • Vaccine ingredients like egg protein or gelatin can trigger allergic reactions in dogs, causing symptoms like facial swelling, hives, or vomiting.1
  • Adjuvants like aluminum hydroxide boost the immune response to vaccines. But in some dogs, they may overstimulate the immune system and cause inflammation or autoimmune reactions.2
  • Each dog has a unique immune system. Reactions are idiosyncratic responses tied to individual immune function and genetics.

Understanding the mechanisms behind vaccine reactions allows vets to take steps to prevent or manage them through careful vaccine selection, administration, and monitoring of dogs.

Risk Factors for Reactions

Certain dogs may be at higher risk for experiencing adverse reactions to vaccines. Some of the main risk factors include:

woman with small dog breed chihuahua

  • Breed – Small breeds like Chihuahuas, Dachshunds, and Pomeranians tend to be more susceptible to vaccine reactions compared to larger breeds. Herding breeds like German Shepherds and Australian Shepherds are also at increased risk (
  • Age – Young puppies receiving their initial series of core vaccines are at greatest risk of reactions. Vaccines stimulate a robust immune response in young dogs that can sometimes lead to adverse events (
  • Past reactions – Dogs with a history of vaccine reactions are more likely to experience future reactions. Reactions can become more severe with repeated vaccinations (
  • Health status – Dogs that are immunocompromised or suffering from chronic disease may not respond well to vaccines. Certain medications can also suppress the immune system and increase risk.
  • Genetics – Some dogs may have a genetic predisposition that makes them more prone to vaccine hypersensitivities and immune-mediated disorders.

Preventing and Managing Reactions

There are several steps dog owners can take to help prevent vaccine reactions in their pets:

Prescreening – Prior to vaccination, a veterinarian should perform a full physical exam and obtain a medical history. This allows the vet to identify any pre-existing conditions that may increase the risk of an adverse reaction.

Separating vaccines – Administering individual vaccines several weeks apart, rather than multiple vaccines on the same day, can help reduce the likelihood of reactions. This “limited antigen” protocol gives the immune system more time to respond to each vaccine appropriately [1].

Using only necessary vaccines – Following published vaccine guidelines helps ensure dogs only receive vaccines that are recommended for their age, breed, and lifestyle. Overvaccination can trigger unnecessary immune system activation.

Avoiding unnecessary adjuvants – Adjuvants ramp up the immune response but may increase reactogenicity. Core vaccines without adjuvants tend to produce fewer side effects.

Monitoring post-vaccination – Pet owners should monitor their dog closely for several hours after vaccination for signs of anaphylaxis or other acute reactions. Mild delayed reactions may occur up to 3 weeks later.

Treating reactions – For mild reactions, antihistamines and anti-inflammatories may provide relief. More severe reactions require swift veterinary intervention with epinephrine, steroids, intravenous fluids, and supportive care. Reactions should be reported to the vaccine manufacturer.

Titer testing – Antibody titer tests help determine if an animal already has sufficient immunity without revaccination. This may be recommended for dogs with a history of vaccine reactions.

The Importance of Titer Testing

Titer testing can be an important tool to determine if your dog actually needs a vaccine booster. Rather than automatically revaccinating per the vaccine manufacturer’s recommended schedule, a titer test measures the level of antibodies still present in your dog’s bloodstream. If antibody levels are sufficient, revaccination may be unnecessary as the dog is already protected. As noted in this DogTime article, some research indicates immunity may last many years or even be lifelong for some diseases after the puppy vaccine series.

veterinarian performing antibody titer test

According to veterinarian Jean Dodds in an article from Dogs Naturally Magazine, using titers instead of automatic revaccination can help prevent adverse vaccine reactions in susceptible animals. Titers may be especially useful for dogs who previously had a reaction or those at higher risk due to age, breed, or medical conditions. Discuss titer testing with your veterinarian to determine if it’s appropriate for your dog.


While some vaccines can cause adverse reactions in dogs, the benefits of vaccination far outweigh the potential risks. Vaccines prevent serious and often fatal infectious diseases like distemper, parvovirus, rabies, and kennel cough. Reactions are relatively rare and generally mild. Severe reactions are very uncommon. By working closely with your veterinarian and following their recommendations, you can protect your dog against disease while minimizing any risks.

There are things pet owners can do to reduce the chances of vaccine reactions. Only giving necessary vaccines, separating vaccines into different appointments, and titer testing can all help. If a reaction does occur, veterinary care can treat symptoms and manage any complications. With vigilance and care from pet owners, vaccines remain one of the best defenses for canine health.

The key takeaway is to not avoid or fear vaccination due to the small risk of reactions. The benefits far outweigh the potential downsides. Work with your vet to create the optimal vaccination schedule for your dog. Stay informed on the latest vaccine research and guidelines. Report any reactions promptly so your vet can respond appropriately. With smart precautions and care, you can safely protect your dog against disease through vaccination.

dog vaccination schedule chart

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