Dog and Cat Vaccination FAQ

Monica Tarantino, DVM
By Monica Tarantino, DVM on Jul. 16, 2019

Vaccination FAQs

Jump to a specific question and answer:

1. My pet has always had a reaction to vaccines; what causes this?

2. How safe are pet vaccines? Do they cause cancer, illness or fatal side effects later?

3. Which vaccines are really necessary for cats/dogs?

4. Is it possible to over-vaccinate?

5. Are there any vaccines that are no longer necessary?

6. How long do the vaccines stay in your pet’s system?

7. Why aren’t pets titered to determine if a vaccine is necessary?

8. Why are there two versions of the rabies shot—1-year and 3-year?

9. How often do pets have to get vaccines? Why do they need boosters?

10. What do vaccines cost?

11. Do indoor pets need vaccines? Or are some optional?

12. Does my older Saint Bernard (or any senior dog) need to keep getting distemper shots?

13. Which vaccines do pets need to travel to Europe?

14. Is the leptospirosis shot necessary for city dogs?

15. How are vaccines produced?

16. How are vaccines checked for quality assurance?

17. Is it safe for senior/geriatric pets to get vaccines? (10+ year-old dog or cat)

18. Does the leptospirosis vaccine cause seizures in Dachshunds or other small dogs?

1. My pet has always had a reaction to vaccines; what causes this?

Vaccines contain small particles of virus or bacteria to teach your pet’s immune system how to respond in case of exposure to disease. Though today’s pet vaccines have an excellent safety record, we can never eliminate the risk of side effects 100 percent, and some pets may develop a reaction.

The most common type of vaccine reactions seen in pets are allergic reactions. These happen when the body elicits an exaggerated response. Fortunately, the vast majority of these reactions will resolve with minimal yet timely treatment by your veterinarian. 

In many cases, pets that do react can be safely premedicated prior to future vaccines to prevent or limit the reactions. In other cases, your veterinarian may just recommend avoiding the reaction-inducing vaccine for your pet altogether. 

Let your veterinarian know right away if you suspect a vaccine reaction or if your pet has a history of vaccine reactions.

Keep in mind that modern vaccines have come along way, and though they are not without risk, they are considered very safe for most pets.

Discuss any concerns with your veterinarian, but understand that it’s far more likely that an unvaccinated animal will die of a preventable disease than a vaccine would cause a life-threatening reaction.

2. How safe are pet vaccines? Do any vaccines cause cancer or other illnesses later in life? Are there dangerous/fatal side effects?

Vaccine reactions are relatively rare in pets. Data varies, yet one major study found that in over 1 million vaccinated dogs, only 4,678 had a vaccine reaction.

That translates into roughly 38/10,000 (0.38 percent) of dogs having a vaccine reaction. Studies have shown similar rates for cats.

In general, modern vaccines are considered very safe for your pets, though there will always be some pets that may have reactions. 

Risk of Diseases From Pet Vaccines

Lately, there has been a lot of fear regarding vaccines; however, they continue to be very safe—and possibly the most important—procedures that you can do for your pet. 

Nonetheless, they do not come without risk. Here are some of the diseases that come up when discussing vaccines:

  • Vaccine-induced anaphylaxis (a severe allergic reaction)
  • Feline injection-site sarcoma (rare skin tumor formation)
  • Autoimmune disease in susceptible pets

Vaccine-Induced Anaphylaxis:

Anaphylaxis is a severe allergic reaction that can be life-threatening. 

Most people will think of anaphylaxis in reference to bee stings or peanut allergies. In rare cases, they can occur in response to vaccines in pets, typically within minutes to hours of vaccine administration.

If you notice vomiting, diarrhea, hives, swelling, collapse or difficulty breathing, contact your veterinarian right away.

Feline Injection-Site Sarcomas (FISS):

These are rare cancerous skin tumors that can develop months to years after injections in cats. 

At this time, it is thought to be an inflammatory reaction to injections; however, research is still pending to determine exactly why FISS develops in certain cats.

Sarcomas are serious cancers of the skin and must be treated aggressively, but research indicates that the risk of FISS in cats is lower than the average risk of other reactions in pets at 1/10,000 (0.01 percent). 

Talk to your veterinarian if you notice a lump on your pet, especially if it appears in the area of the vaccine administration. 

Autoimmune Disease in Susceptible Pets:

The concern of autoimmune disease developing from vaccines has been a hot topic. 

The truth is that the overwhelming majority of vaccinated animals do not develop autoimmune disease. The risk of not vaccinating is far greater than the likelihood of vaccine reactions or vaccine-induced disease.

Veterinarians do recognize that there are some cases of autoimmune disease that seem to develop following vaccination.

However, to date, research still does not prove that vaccines are the cause of autoimmune disease in pets. Research is ongoing, but the suspicion is that autoimmune disease in pets is caused by a combination of factors that include genetics, environment, etc.

If your pet has already been diagnosed with an autoimmune disease—like immune-mediated hemolytic anemia (IMHA) or immune thrombocytopenia (ITP)—it is likely that your vet will take precautions and only vaccinate if necessary.  

Pets with existing autoimmune disease are at greater risk for vaccine reactions.

3. Which vaccines are really necessary for cats/dogs and which are optional?

Necessary vaccines for cats and dogs are called ‘core’ vaccines. Noncore vaccines are considered optional and are recommended based on lifestyle and other factors. 

Dog Vaccines

Core Vaccines

Rabies vaccine and Distemper/Adenovirus/Parvovirus (DAP) vaccine

Noncore (Optional Vaccines

Bordetella vaccine, Leptospirosis vaccine, Lyme vaccine, Canine Influenza vaccine

Cat Vaccines

Core Vaccines

Feline Rabies vaccine, Feline Panleukopenia/Herpesvirus-1/Calicivirus (FVRCP) vaccine

Noncore (Optional) Vaccines

Feline Leukemia Vaccine

4. Is it possible to over-vaccinate?

To help prevent over-vaccination, a set of guidelines for both cats and dogs have been developed by veterinarian experts:

These guidelines incorporate the latest scientific data on vaccines and pet health. They help promote a standard of care that allows us to protect our pets from disease while limiting possible complications from vaccination.

As always, discuss vaccines with your veterinarian to determine what is right for your pet.

5. Are there any vaccines that are no longer needed based on recent changes/findings?

Core vaccines such as rabies and distemper will always be needed, as even with our best vaccine protocol, these fatal diseases widely exist and have the potential to be devastating for our pets and wildlife.

In the case of rabies, this disease can also pose a risk to you and your family.

Noncore vaccines will be recommended based on the lifestyle and risk level of your pet. Some vaccines that have fallen out of favor include:

6. How long do the vaccines stay in your pet’s system?

Depending on the age and timing of vaccine, the immune response generated by vaccines can be anywhere from weeks to years.

Younger pets (puppies and cats) will need vaccines more frequently due to antibodies provided by their mother that minorly interfere with a vaccine’s long-term effectiveness. Older pets can have a lasting immune response that will stay effective for months to years.

7. Why aren’t pets titered to determine if a vaccine is necessary?

Some veterinarians may offer checking titers for vaccines. An “antibody titer” can help to determine if a pet still has protective immunity from a vaccine. 

Antibody titers measure the level of antibodies in your pet’s blood for certain viruses or bacteria. Antibodies (immune system proteins) are “memory” proteins that are on the lookout for viruses and bacteria that are trying to infect a pet’s body. 

Antibodies are specific, and once they find an offending invader, they tag them for destruction and alert the body to mount an attack on the invader bacteria or virus.

Vaccines help stimulate antibodies so that your pet’s body can recognize foreign invaders quickly and defend itself. So antibody titers can be used to determine if your pet’s immune system is at a level where it would generate an appropriate immune response to possible infectious diseases.

Titers could be specifically useful to pets that are known to have vaccine reactions or already have an established autoimmune disease.

Limitations of Antibody Titers for Pets

Titers can be a good option for some pets, but there are limitations that are important to be aware of:

  • Antibody titers are only considered an option for the core DAP vaccine (distemper virus, canine parvovirus and canine adenovirus).

  • There can be false positives, which could indicate that your pet has protection when it might not.

  • There can be false negatives, causing a vaccine to be administered to a pet that had adequate immunity anyway.

  • Doing a single titer will not tell you when your pet will lose immunity. This means that having a positive antibody titer test on one day does not mean that it will be  positive the next.

  • Legal issues with rabies titers: most jurisdictions do NOT allow a rabies titer to be done in lieu of the vaccine. In most states, your veterinarian does NOT have the discretion to waive a rabies vaccine.

  • Titers can be costly (usually between $125-200), but this depends on your veterinarian and which titer test they use.

If you are interested in a titer, please discuss it with your veterinarian, who can help determine your pet’s needs. AAHA has come out with a detailed discussion and guide on titers in pets.

8. Why are there two versions of the rabies shot—one that lasts a year versus one that lasts three years? Is the 3-year vaccine dosage harmful for pets?

There are multiple rabies vaccines that are licensed for pets in the US. Some of the vaccines will give immunity to our pets for one year, while others will provide it for three years. 

The first rabies vaccine for your pet will always be a 1-year and requires a booster one year later.  

Though this depends on the manufacturer of the vaccine, often 3-year vaccines have more antigens than 1-year vaccines. 

Vaccines labeled for three years are used commonly and are generally not considered more harmful to your pets.

9. How often do pets have to get vaccines? Why do they need boosters? How many are 3-year vaccines?

Most vaccines in adult pets are given every year or every three years depending on the vaccine and vaccination status of the pet. If your pet has never been vaccinated before, a booster vaccine following the initial vaccine may be needed.

Booster vaccines assure that proper immunity and protection develops in your pet. Without the recommended booster, your pet may not be effectively protected. 

Vaccines that can be given every three years include the rabies vaccine, FVRCP vaccine and DAP vaccine. However, the first time these vaccines are given, they have to be given as 1-year vaccines.

10. What do vaccines cost?

Vaccines on average can range anywhere from $15-35 depending on the vaccine and formulation.

Prices will vary based on the location and the services offered.

11. Do indoor pets need vaccines? Or are some optional?

Indoor-only pets still need to stay up to date with core vaccines and yearly exams.

An unintended, though common, problem we see with indoor-only pets is that they accidentally get out. And if they are unvaccinated, it means they can be exposed to disease with no protection at all. 

In addition, it is possible for owners or other pets to expose indoor-only pets to disease. Some diseases are in the environment and can be brought in by owners or other pets.

Other diseases are so dangerous to people, such as rabies, that it is mandated by law to have all animals vaccinated for this disease.

12. My Saint Bernard is 8 years old and has had all her distemper shots. Does she (or any senior dog) need to continue getting them?

Data has shown that distemper vaccines in our pets often last longer than three years—which is great—but because every pet’s immune system is different, there is no guarantee your dog will be protected from distemper. 

Vaccines in older pets are considered very safe. If you are concerned about over-vaccinating, my recommendation is to discuss the option of a titer with your vet.

It may still be their recommendation to vaccinate (as titers do not come without downfalls), but titers could be an option for an older pet. 

As always, discuss this with your veterinarian to see if this makes sense for your pet.  

13. Which vaccines do pets need to travel to Europe?

Vaccine and other requirements needed for pets to travel to Europe with you depend on which country you are traveling to.  

Most countries will require up-to-date rabies vaccines and a microchip in your pet, but it is VERY important to look into requirements as early as possible before your trip.

Documentation and steps will vary by country. More info can be found on the United States Department of Agriculture (USDA) website.

In addition, some owners may want to consider working with an expert in pet travel. Though this may seem excessive, the process of bringing a pet abroad can be challenging and stressful, and pet travel experts can help in these situations.

14. Is the leptospirosis shot necessary for city dogs?

Leptospirosis traditionally was thought of as a disease in rural areas; however, this is changing. 

In busy cities, leptospirosis can be spread to dogs via rodents and city wildlife and areas of standing water.

Dr. Rudy E. Zamora, a veterinarian in NYC reports, “There are cases of canine leptospirosis every year because of the rat problem here. I had a patient die at the ER last year that was a confirmed leptospirosis case.”   

According to a leptospirosis FAQ published by NYC's official website, the city averages about 10-20 cases a year, with most cases being centered in Manhattan. The city of Boston had an outbreak of canine leptospirosis in 2018.  

I encourage you to discuss the leptospirosis vaccine with your veterinarian to determine if it is right for your pet. The leptospirosis vaccine has improved drastically in the past decade, making it less immunogenic, which in turn causes fewer possible side effects.  

Pets that contract leptospirosis often become very ill and have to be hospitalized for multiple days while they recover.

Additional consideration for leptospirosis is that it is a disease that’s transmissible to people as well. So it is even more important if you have small children, older adults or immune-compromised family members living in your home.

15. How are vaccines produced?

In order to produce vaccines, viruses are introduced into cell cultures to produce viral antigens—the main component of the vaccine. 

These are then harvested, and viruses are either killed or modified into an inactive state for vaccine safety.  

A process of purification to remove cellular debris and stabilization will occur as well as a process to quantify vaccine concentration before forming the end product. These processes are performed to assure safety, stabilization and effectiveness of the vaccine end product.  

16. How are vaccines checked for quality assurance? Is this done through pharmaceutical companies who are biased?

Government oversight and regulation of vaccines for pets is performed by the United States Department of Agriculture (USDA).

This means that manufacturers of vaccines must adhere to rules and regulations established by the USDA in creating safe and effective vaccines that do what manufacturers claim they do.  This includes quality control monitoring by the USDA.

There are multiple large pharmaceutical companies, which allows for a healthy amount of competition to assure constant refining and improvement of vaccines, as no company wants to be outdone by the other.

So far in our US market, I believe this has helped produce pet vaccines that the majority of veterinarians consider to be very safe and efficacious. 

17. Is it safe for senior and geriatric pets to get vaccines? (10+ year-old dog or cat)

Yes, it is still considered safe for senior and geriatric pets to get vaccines. Discuss with your veterinarian which vaccines they recommend for your senior pets.

The goal with every pet is to keep them healthy and protected while not over-vaccinating. Your veterinarian can help you figure out what that means for your pet and will review their history, current disease/illnesses, lifestyle and risk to help determine which vaccines are appropriate for your older pet.  

Distemper titers can be discussed with your vet as well.          

18. Does the leptospirosis vaccine cause seizures in Dachshunds or other small dogs?

Unfortunately, there are no studies on leptospirosis vaccines inducing seizures in Dachshunds. 

We do know, however, that smaller dogs (under 10 kilograms or 22 pounds) that receive multiple vaccines during a single visit are more likely to have reactions than the general population. 

There is no number of vaccines that is the “cutoff.” But if your small breed dog is due for numerous vaccines, your vet may recommend splitting up vaccines between two visits that are two weeks apart.

By: Dr. Monica Tarantino, DVM

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Monica Tarantino, DVM


Monica Tarantino, DVM


Dr. Monica Tarantino is a small animal veterinarian and pet parent educator. She's on a mission to help senior cats and dogs around the...

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