• Thu. May 23rd, 2024

What is Over-Vaccinating Your Cat? Vet-Approved Explanation


Mar 3, 2023
The veterinarian gives the drug to the cat with a syringe


The veterinarian gives the drug to the cat with a syringe
Dr. Lorna Whittemore Photo

The information is current and up-to-date in accordance with the latest veterinarian research.

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Like most cat owners, you likely take your cat in for preventative care at the veterinarian clinic every year. This is also when they receive their annual vaccines. But have you ever wondered how necessary a vaccine is, especially if you have an indoor cat?

Some owners have concerns about “over-vaccinating” cats, so let’s look at how vaccines are beneficial for cats, along with the risks. Over-vaccinating happens if cats are unnecessarily vaccinated for illnesses that they are not at risk from, and at a higher frequency than what is suitable to maintain immunity.


How Do Vaccines Work?

Vaccines generally work by injecting small amounts of pathogens, such as bacteria or viruses, that stimulate your cat’s immune system1. This way, the body will have increased immunity to the full virus or bacterium if or when it encounters it in the future.

The vaccine essentially imitates an actual infection, which helps the body to be better protected in the future. It can either stop the infection altogether or lessen its severity.

cat vaccination
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divider-catVaccine Types for Cats

There are core vaccines that most vets will recommend for cats, along with non-core vaccines.

Core Vaccines (Recommended)

The following are the vaccines that your cat will typically receive during their annual wellness check-up and are recommended by the World Small Animal Veterinary Association.

Feline herpesvirus 1 infection (FHV-1). It affects the upper respiratory tract and the eyes and is easily transmissible to other cats through any infected secretions from the mouth, nose, and eyes. The most common symptoms are sneezing and nasal discharge.

Feline calicivirus (FCV) is another infection that affects the upper respiratory tract and tends to resemble a cold1. But it can present as a more serious infection in the joints, lungs, and other organs. Cats can catch this virus the same way as with FVR, through secretions.

Feline panleukopenia (FPV) is also known as feline distemper or parvo2. It is highly contagious and is frequently fatal even with treatment. It is highly contagious. FPV is also passed through bodily secretions such as urine, feces, saliva, and vomit.


Most people are familiar with rabies. It’s caused by a bite from an infected animal—most commonly in North America, a bat—and is almost always fatal. Most municipalities require all cats and dogs to get the rabies vaccine annually as it is a risk to humans.

Non-Core Vaccines (Optional)

The non-core vaccines are also referred to as lifestyle or situational vaccines. These are only given to your cat based on the individual cat’s situation and their daily activities.

  • Feline leukemia (FeLV) is transmitted by saliva and can be passed to an infected mother’s kittens3. The worst thing about this virus is when a cat becomes infected, you won’t know, and once the symptoms start appearing, it’s almost too late to treat the cat.
  • Chlamydiosis infection affects the respiratory system and like some other infections, will present as a cold, with sneezing, runny nose, and watery eyes4.
  • Feline infectious peritonitis (FIP) is a feline coronavirus that is spread through contact with contaminated feces5. It’s only contagious to other cats, starting as a coronavirus and sometimes turning into FIP. FIP is often fatal and treatments are currently very expensive and experimental. (Discuss the efficacy of this vaccine with your veterinarian).
  • Bordetella bronchiseptica (Bb) is a respiratory infection that results in coughing, sneezing and ocular discharge.
cat getting vaccine in a vet clinic
Image Credit: Africa Studio, Shutterstock


Side Effects of Vaccines

Vaccines have been instrumental in helping the prevention of deadly and highly infectious diseases in cats. The vast majority of cats receive vaccinations with no reported side effects or concerns. In fact, only 0.52% of vaccinated cats were reported to have had any kind of reaction in the 30 days following vaccination. Most of these reactions were mild and similar to what we experience as people.

Vaccine-Associated Adverse Event

When dogs or cats suffer from adverse effects from vaccinations, it should be reported to your veterinary surgeon. This includes severe reactions such as anaphylactic shock, and lesser ones such as temporary low-grade fever.

Cats with compromised immune systems are more prone to vaccine-associated adverse events. This is why it is not recommended to vaccinate your cat if they are currently unwell.

sad lonely cat
Image Credit: medveda, Shutterstock

Minor Side Effects

Minor transient side effects can include the following:

  • Minor swelling, tenderness, and redness at the injection site
  • Fatigue
  • Low-grade fever
  • Reduced appetite

Contact your vet if these side effects worsen or last more than 24 hours. If a firm and small bump does appear at the injection site, it should vanish within 2 weeks. But if it gets worse or lasts longer than 3 weeks, speak to your veterinarian.

Allergic Reactions

Allergic reactions aren’t common, but they can occur in minutes to several hours after the vaccination. If your cat exhibits any of the following signs, treat it as a medical emergency, and bring them to your vet or the closest emergency vet clinic immediately.

  • Difficulty breathing
  • Fainting or collapse
  • Hives (small, raised, itchy, and red bumps on the body)
  • Puffy or swollen eyes, face, or muzzle
  • Persistent vomiting and diarrhea

If your cat has had bad reactions to vaccines before, let your vet know, and stay at the clinic for at least 30 minutes to an hour after their vaccinations.

a cat that feels sick and seems to vomit
Image Credit: chie hidaka, Shutterstock


What Is “Over-Vaccinating”?

Frequency of Vaccination

Vaccines are designed to stimulate the cat’s immune system to produce antibodies, which react to foreign organisms, like viruses, in the bloodstream. This way, the body will recognize the actual organism when exposed to it and will produce the right antibodies to inhibit or remove the virus.

The idea of “over-vaccinating” is based on the premise that cats should only be vaccinated for illnesses that they are at risk from, and at a frequency that is suitable to maintain immunity and not more frequently than this.

Many adult cats don’t necessarily need to be given booster shots every year but should still have an annual health check. Some cats can benefit from annual vaccines if they are at higher risk such as in a boarding facility or spend time outdoors with other cats for example. But annual vaccines aren’t always necessary for healthy, adult indoor cats. This is because several vaccine brands are available that are required to be given every 3 years to provide protection against Feline Herpes Virus, Panleukopenia and Feline Calicivirus, rather than yearly.

Rabies is a vaccine required by most countries’ laws and the vaccine that your cat needs every year.

Kittens should be vaccinated by a schedule to ensure an adequate immune response: They typically receive their first vaccinations around 6 to 8 weeks, then boosters at 10 to 12 weeks and 14 to 16 weeks, which is followed by a 1-year booster (this 1 year booster is very important).

Following this, many vets recommend that adult cats receive boosters on a yearly or 3 yearly schedule depending on the individual cat risk factors.

Veterinarian at vet clinic giving injection to cat
Image Credit: Tom Wang, Shutterstock

What Are Titer Tests?

Studies have shown that for many pets, the vaccines can last longer than the once-a-year booster, and some can protect the pet for a lifetime. Many vaccines now carry licenses for vaccinating every 3 years for some illnesses.

Titer tests are an alternative to be considered before booster shots for pets. The antibody titer is a blood test that measures the presence of antibodies in the bloodstream for a specific disease. This way, a veterinarian can judge whether the booster is necessary depending on how well-equipped the cat’s immune system is. However, these tests are usually more invasive and expensive than the vaccination itself. They also do not have a predictive effect, they cannot tell you when the immunity will reduce and thus require boosting.



Vaccines are essential for most pets: They effectively protect them against serious diseases and enable them to live happy and stress-free lives. But while most cats do not have any adverse reactions to their boosters, a small percentage (around 0.52%) do.

Talk to your vet about your concerns and about running a titer test if you would like to know more about their current state of immunity. Always speak to your vet so you can discuss what is best for your cat in the long run.

Featured Image Credit: Egoreichenkov Evgenii, Shutterstock

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