cat unwell after vaccination
Cat Health and Wellness

Can Cats Have a Reaction to Vaccinations?

Vaccines are necessary for most cats, especially those who spend most of their time outdoors. Although the experience is never pleasant, felines must be vaccinated against rabies by law. Also, other vaccinations are highly recommended to protect your cat against infectious diseases.

All vaccines have the potential to cause side effects in cats. Fever, lethargy, reduced appetite, and swelling are all very common. Some cats also have trouble walking and experience stomach upsets. These adverse effects should subside after 24 to 48 hours.

There is always risk involved in vaccinating a cat. These dangers alone are not enough to avoid getting feline vaccinations, though. You’ll need to make an informed decision about whether to vaccinate your cat based upon all the available medical evidence.

Types of Vaccinations for Cats

A vet will offer many essential vaccinations for your cat. These protect against the following conditions:

  • Rabies
  • Feline Distemper (Panleukopenia), Feline Herpesvirus (FHV-1), and Feline Calicivirus (FCV)
  • These three vaccines are combined into one (FVCRP vaccine)
  • Feline Leukemia Virus (FeLV)
  • Feline Immunodeficiency Virus (FIV)
  • Feline Infectious Peritonitis (FIP)
  • Bordetella
  • Chlamydophila felis
  • Feline

Of these vaccines, rabies is the only one that is required by law in most U.S. states. Check the status of your state using this table compiled by the American Veterinary Medical Association.

Even if you reside in a state that doesn’t mandate rabies shots by law, it still remains advisable. The disease is commutable among animals and humans.

The American Association of Feline Practitioners also considers the FVCRP to be a core vaccine. Beyond this, all other vaccines are optional.

How are Vaccines Administered to Cats?

Feline vaccinations are commonly administered by injection. The location of the shot is typically behind the legs.

Previously, many vets chose to administer shots to the neck. This was due to the flexibility of the skin in this area. It’s easier to stretch the skin, and administer a shot.

In recent years, the risk of Feline Injection Site Sarcoma (FISS) has become more of a concern. This means the neck should always be avoided. FISS causes a cancerous tumor at the site of the vaccination.

This tumor would need to be removed as quickly as possible if it happens. That can be difficult, and almost impossible to do around the neck.

cat not feeling well after vaccinations

A vaccination against rabies would usually happen in the right back leg. A vaccination for FVCRP would happen in the right front leg.

Not all vaccines must be injected. FVCRP, FIP, and Bordetella can be inhaled nasally, but may not be as effective as injections

If your cat takes its vaccinations intranasally, it will sneeze and sniff for a while afterwards. Some streaming from the eyes and nose may also follow.

What Are the Most Common Side Effects of Cat Vaccinations?

Vaccines are medication, and all medications have potential side effects.

A cat’s immune system starts to adapt following a vaccine. This will mean that a cat will look sick. This is only a concern if it does not quickly recover. Some common side effects of feline vaccination include:

  • Fever
  • Lethargy and low energy levels
  • Lack of appetite
  • Vomiting and diarrhea
  • Swelling around the location of the injection
  • Trouble walking

These side effects should be short-term. If your cat is still unwell 48 hours after its vaccination, then you should call your vet for advice.


As vaccinations are injected into a cat’s leg, some limited mobility is to be expected. Your cat may experience a small amount of swelling at the injection site. This will make it tougher for your cat to move.

The FVCRP vaccine is most likely to cause limping. This is because lameness is a common symptom of feline calicivirus. This is so common that it is called limping syndrome.

Limping syndrome in cats is a temporary problem. Cats that struggle with this side effect bounce back as quickly as they experienced the issue.

Cats that have this vaccination often experience stiffening joints. This will naturally make them more lethargic. Any movement will be painful for the full duration of this side effect.

Your vet may prescribe a painkiller for your cat following its vaccination. This will be safe. Never offer your cat human medication.

Any vaccine can cause some degree of limited mobility. Only the calicivirus vaccine should cause ‘limping syndrome.’

If your cat is limping for more than a day or two, then you should seek medical assistance for your cat. This suggests a more troubling reaction to a vaccination, but such instances are very rare.


Vomiting should be monitored after vaccinations. It is not unheard of, but neither is it entirely commonplace.

Your cat may just be vomiting its previous meal. A cat’s body will go through an adjustment after a vaccine is administered. That can upset your cat’s stomach and cause vomiting.

Diarrhea is also a possibility for the same reasons. However, it’s also possible that your cat is experiencing an allergic reaction to the vaccine.

No Energy

It’s natural for a cat to become listless and sleepy after vaccines are administered. A feline that has been vaccinated will want to be on its own to sleep for several hours. It may also run a high fever.

You need to ensure that your cat is left alone. Tell any children in the home not to disturb your cat. It should be treated as if it has a minor cold.

cat not eating after vaccination

Not Eating

A loss of appetite is a common side effect of vaccination. Any cat that has not eaten for 24 hours is a cause for concern. Cats have small bodies and few fat reserves to sustain them.

Assess whether your cat isn’t eating or is just reluctant to walk to its bowl. If your cat has little energy or limping syndrome, the walk can feel like a long journey, especially for an older cat with joint problems or arthritis pain.

Lump at the Site of The Vaccination

The most alarming reaction to vaccination is Feline Injection Site Sarcoma (FISS). This is a cancerous tumor that develops following inflammation around the site of the injection.

A vet must assess a cat with a substantial lump that persists for weeks after vaccination. Another sign of FISS includes the lump exceeding 2cm in diameter, especially if it keeps growing.

If the sarcoma that is caused by vaccination is not treated, it will grow. This, in turn, will allow cancerous cells to spread. The lungs and other internal organs will quickly be affected.

It is not entirely clear why cats experience FISS. Some experts believe that the felines already have tumors. The inflammation caused by the vaccination activates the malignant tumor and causes it to spread.

If you present your cat to a vet with FISS, urgent surgery will be required to remove the tumor. Your cat may also need to undergo radiotherapy or chemotherapy.

FISS remains rare. The journal Acta Veterinaria Scandinavica has stated that instances remain as low as 1 in 10,000.

Can Cats Be Allergic to Vaccines?

It’s unlikely, but it’s possible for a cat to have an allergic reaction to a vaccination. Cats can be allergic to anything. They could even react to the rubber gloves that your vet wears to administer the vaccine.

An allergic reaction is more concerning than a typical ‘reaction’ to a vaccine. Signs that your cat is allergic to the vaccination include:

  • Hives breaking out on the skin
  • Swelling around the face, eyes, mouth, and neck
  • Trouble breathing
  • A sharp drop in body temperature around the tail and paws
  • Low blood pressure and decreased heart rate
  • Seizures and collapse

These reactions will be treated with steroids or antihistamines. These reduce the ill-effects of the allergy. In more severe cases, your cat may require intravenous fluids and further observation.

Cat Personality Changes After Vaccination

Some cats are temporarily different or never quite the same after vaccination. It’s extremely rare, but it does happen.

This is because the vaccine causes a chemical reaction in a cat’s brain. This normally lasts for around 48 hours.

cat limping after vaccination

If your cat seems to have undergone a complete personality transformation, seek further guidance from a vet.

Make a note of all the changes to your cat’s behavior and look for a pattern. If a vet cannot help, consider consulting a feline behaviorist.

What Are the Side Effects of Vaccinations for Senior Cats?

Older cats have weaker immune systems and are more prone to illness. On the other, they’ll be worse affected by any of the side effects.

If your elderly cat has a chronic illness, then you should avoid vaccination. These treatments can aggravate problems with the heart and kidneys.

If your cat has tolerated vaccinations well in the past, then there is no reason to deny it boosters, provided that its health hasn’t recently faltered. It’s advisable to get your cat inoculated if your cat roams outside.

Respiratory illnesses, which certain vaccinations protect against, can be lethal for senior cats. You can find out more about infectious upper respiratory disease at Today’s Veterinary Practice (TVP).

Cats can, and likely will, react to vaccines. This is an unavoidable side effect of the process. These reactions should not be severe. In most cases, the risks are outweighed by the safety that vaccines provide.