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Vaccine Allergy in Cats

Vaccine Allergy in Cats - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Vaccine Allergy?

An allergy to a vaccine can occur in your cat when his body rejects one or more of the ingredients that make up the vaccine. The purpose of a vaccine is to prevent a particular infection or disease by using antibodies that are similar to the infection or disease to be prevented in order to stimulate the immune system.  

Through the vaccine, your cat’s immune system will be exposed to a particular condition and will be prepared to fight it off should the condition present itself in the future. Sometimes, however, stimulating the immune system will lead to a reaction of some sort, which can be considered a vaccine allergy.

An allergy to a vaccine will occur when, upon injection, your cat’s body rejects one or more of the ingredients that are present in the vaccine, leading to a number of possible symptoms.

Symptoms of Vaccine Allergy in Cats

Symptoms of a vaccine allergy in a cat will be dependent upon the particular vaccine, the breed of the cat and whether the reaction is mild, moderate or severe. A mild allergy is most common; in a mild allergy the symptoms will resolve themselves and can include:

  • Fever
  • Sluggish behavior
  • Sneezing about four to seven days after having received an intranasal vaccine
  • Lack of appetite
  • Soreness or inflammation at the place where the injection occurred
  • Rarely, neurological or respiratory issues may occur

The following symptoms may be present in a moderate allergy to a vaccine:

  • Sneezing
  • Itching
  • Quick swelling
  • Hives
  • Redness of lips, eyes and neck

Should your cat experience a severe allergy to a vaccine, which is rare, he may experience anaphylaxis or anaphylactic shock. This will typically occur within a few minutes through an hour after injection. Symptoms of anaphylaxis include:

  • Trouble breathing
  • Vomiting 
  • Diarrhea
  • Quick drop in blood pressure 
  • Seizures
  • Cardiovascular collapse
  • Inflammation of the larynx
  • Death

Sarcoma, an aggressive form of cancer, is a possible rare side effect from a vaccine. The most seen symptom of sarcoma is a lump where the injection was administered. 


Your cat can experience a mild, moderate or severe allergy to any vaccine that is administered, as well as a sarcoma. Mild reactions will be seen within several hours to several days after the vaccine is administered and will typically last no more than a few days. Should your cat experience a severe reaction, it will be seen within several minutes to an hour after he has received the vaccine. In the case of a sarcoma, the tumor can develop at the vaccination site anywhere from several weeks, months or even longer after it was administered.

Causes of Vaccine Allergy in Cats

An allergy can result in your cat due to the following:

  • A reaction to the live virus in the vaccine
  • The presence of the chemical compounds that have been included in the vaccine to increase its effectiveness
  • Its breed: cats that are purebred are more likely to experience an allergy
  • Several vaccines being administered at one time
  • Your cat can become sensitized to the ingredients in the vaccine, which can lead to an allergy upon vaccination in the future

Diagnosis of Vaccine Allergy in Cats

Should you notice symptoms of anaphylactic shock, it is imperative that you get your cat medical attention immediately as this can be fatal. Upon your arrival, the veterinarian will first focus on stabilizing your cat, and conduct a thorough examination of him. This will include measuring his heartbeat, taking his blood pressure and looking to see if your cat has hives or trouble breathing, among other concerns. You will be asked about the symptoms that your cat is experiencing, when you first noticed them and if any change has occurred. You will want to be prepared to provide information on any medications or supplements your cat takes, details about his diet, and whether and when he received a vaccination. If you have seen your cat experience ongoing vomiting or diarrhea, it is important to let your veterinarian know as this will point to anaphylactic shock. 

Should you notice a lump at the place where your cat’s vaccine was administered, you will want to bring it to your veterinarian’s attention. After conducting a physical examination, your veterinarian may consider a biopsy (particularly if the lump is more than 2 cm, has been present for more than a few months, and continues to grow). The biopsy will allow for the contents of the lump to be tested.

Treatment of Vaccine Allergy in Cats

Should your cat experience a mild allergy, no treatment is typically necessary. In a more moderate allergy, antihistamines will be tried first. Should they not alleviate the symptoms that your cat is experiencing, your veterinarian will likely recommend steroids. In severe allergies, your veterinarian will typically give your cat steroids and antihistamines. Depending on the symptoms that your cat is experiencing, oxygen and intravenous fluids may also be administered. If your cat develops sarcoma, your veterinarian will consider chemotherapy or radiation therapy, as well as amputation of the impacted limb.

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Recovery of Vaccine Allergy in Cats

If your cat experiences a mild allergic reaction, he will recover with a good prognosis. It is a good idea to keep an eye on your cat to make sure that he does not develop anaphylaxis. Should your cat develop anaphylaxis, if he receives immediate medical attention he will be able to recover. Upon receiving supportive care and necessary medication, the allergic reaction will begin to reverse itself. Your veterinarian will want to be sure that your cat can receive future vaccines without a significant reaction.

It is recommended that your cat receive future vaccines with a killed virus rather than a live one and on a less frequent basis (and with only one vaccine administered per visit) and without adjuvants in order to reduce the chance of an allergy. You will want to communicate with your veterinarian and maintain follow up appointments as requested to ensure the best outcome for your cat.

Vaccine Allergy Questions and Advice from Veterinary Professionals


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Seven Months


0 found this helpful


0 found this helpful

My pet has the following symptoms:
Sad No Purring Or Playing
Our kitty got his 6 month vaccines on Wednesday of last week, he developed a high fever 2 days later. And that went down after getting subQ fluids but he still isn’t purring or playing much, should I be worried

Sept. 27, 2020

Answered by Dr. Michele K. DVM

0 Recommendations

Thank you for your question. I hope that he is feeling better. Some animals do have reactions to vaccinations, and if he is not back to his normal self, It would be best to have him seen by a veterinarian, as they can examine your pet and see what might be causing this, and let you know what treatment might help.

Oct. 11, 2020

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1 Year


2 found this helpful


2 found this helpful

My pet has the following symptoms:
Won’T Eat
Won’T Drink
Hiding. Antisocial
No Bathroom
My cat got a vaccine today at 8am and went under our bed to sleep around 10am once we got home and will not move from under the bed. It’s been almost 14 hours.

July 19, 2018

2 Recommendations

There are a few different reactions which may occur after vaccination including lethargy; however if Willow is extremely lethargic or isn’t responding to being called you should take them back to your Veterinarian for an examination to be on the safe side. Regards Dr Callum Turner DVM

July 19, 2018

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