Side Effects of the Feline Leukemia Vaccine

| Modified on Nov 05, 2017

Feline Leukemia is a dreaded and serious viral disease. It is contagious, but only from cat to cat. Cats transmit the disease to one another through shared water bowls and litter pans, grooming one another, bites, and mothers can transmit it to their babies. Symptoms of Feline Leukemia include lethargy, swollen lymph nodes, abscesses, diarrhea, fever, and anemia. While there is a vaccine for feline leukemia, mild and serious side effects from the vaccine are not uncommon.

Sometimes, side effects are comparatively mild. Swelling at the site of the vaccination, fever, lethargy and behavior changes are some of the milder reactions.

Reports From Earth Clinic Readers

Joann, from Atlanta, Georgia, reports to Earth Clinic, "My 5 year old cat received a feline leukemia booster yesterday. He was acting himself prior to the vaccine. I did this because I have a rescue cat which may be leukemia positive; because of this I have given boosters to the other cats. This morning, I found him hiding in the closet. He is growling and not very approachable. He will not eat now. I have never seen him like this."

However, for other cats, one side effect of the vaccine is as serious as the disease the vaccine was given to prevent. One Earth Clinic contributor had a cat that developed a dangerous cancerous tumor, or sarcoma, at the site of the leukemia vaccine.

Avoiding Side Effects of the Leukemia Vaccine

Cats should be tested for the feline leukemia virus before they are given a vaccine for it. Indoor cats, who are not exposed to other cats, are unlikely to contract feline leukemia.

A sick cat should not be vaccinated. It is best to avoid vaccinating a cat in conjunction with a surgery. While it might mean one less trip to the vet, a cat that is recovering from surgery, and thus already under stress, is more likely to have side effects from a vaccine.

Treating Side Effects of the Feline Leukemia Vaccine


Thuja is a homeopathic remedy commonly given to pets when they have side effects from vaccinations.

Activated Charcoal Powder

Activated Charcoal Powder can be given for diarrhea, vomiting, and to detoxify from the vaccination.

  • Mix 1/4 teaspoon of charcoal powder into some water and administer with a syringe.
  • If the cat is eating, it can be mixed with wet food.
  • This can be given every few hours.

Prevent Dehydration

A cat with vomiting or diarrhea should be monitored for dehydration. Giving small amounts of liquid by syringe very often may be necessary.

Colloidal Silver

If the site of the vaccine becomes infected, colloidal silver can be sprayed on the area several times a day.


Honey is another safe topical treatment for a skin infection.

If your cat experiences side effects from the feline leukemia vaccine, please be sure to share your experience!

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13 User Reviews

Posted by Connie (Nc) on 11/04/2017

I purchased a purebred male Russian White feline, DOB 3-26-17. Brought him home at 8 weeks old. Beautiful, extremely energetic, playful and very affectionate. Gave him the recommended vaccines at 10,12,16 weeks. I separated the Rabies to give it by itself as well as the first feline leukemia vaccine, 2 weeks after rabies. All vaccines before the FeLV seemed to agree with him. About 1 hour after the first FeLV shot on Aug 21st, he was lethargic and just plain didn't feel good for about 36 hours. Then 3 weeks later I let the vet give him the booster. He quit playing, just wanted to sleep and be held. Then, about 2 weeks later he developed severe diarrhea, had blood in the stool, and vomited several times and virtually stopped eating. After numerous attempts to find something he would eat, he seemed to feel really hot, so I took him back to the vet on Sept 21st and $2200.00 later, I still had no definitive diagnosis of what was wrong with the little fellow. He still, at 6 months old, didn't weigh 5 pounds yet and was getting worse. Vet wanted to send me to an internal medicine specialist so they could "do more tests" when I knew in my heart that it was a severe reaction to the FeLV. Things were way too coincidental with the timing of the vaccines. I agreed to take him to the internal medicine specialist, first available appt was for Nov 9th. I took him to a second vet in the meantime on Nov 1st, thinking he was constipated since his little belly was very distended. This vet did an abdominal tap and found fluid and blood in the peritoneal cavity. Not a good sign. Gave rectal enema for some relief and low dose steroid shot. I tried everything, even water with baby syringe. He got weaker and weaker. He died Nov 4th before I could get him to the specialist.

If you are thinking about giving the FeLV for your indoor only cat, I hope my experience will help you make your decision easier.

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Posted by Diane (Tx) on 01/14/2017

My (indoor) cat received the first of 2 vaccinations in the morning. About mid afternoon he started sleeping more than usual, wouldn't eat or drink water, and cries when picked up, no matter how careful we are. It's now 3 am and I got a small amount of water in him with children's syringe. As much as he'd allow. I'm hoping this will pass. I will try again with the water in the morning. He is strictly an indoor cat, no contact with other animals of any kind. But I stupidly didn't research the leukemia vaccine. I would never have had him get this vaccine. I do blame myself for going in blindly. It was so unnecessary. I hope this helps someone else. I'm praying he makes it through this, after reading other stories of bad effects with other's cats. Bless you all.

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Posted by Jen (British Columbia) on 09/07/2016

Our kittens are just shy of months old. They both received the Feline Leukemia Vaccine yesterday around 4pm. This morning, the female was fine. She slept straight through from coming home and until 6am. The male... is still sleeping. He sort of woke up. Just sorta sat there. He began to take a few steps and is now limping and seems very lethargic. The first thing I did was give him a few doses of H2O via a syringe. 'Both' cats are very healthy cats! The male is a great climber and the crazier and heavier of the two. There is no reason for the limping as they went straight from vet to home to sleep. I was reluctant to get the vaccine in the first place, but they are in love with the outdoors. Now, I am on the hunt for Thuja and anything else I can do to make the little guy comfortable. They're supposed to get a booster in 1 month. Uggg.

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Posted by Carey (Mi) on 05/04/2016

I decided to give my indoor outdoor beautiful black 2 year old cat the leukemia Vaccine. He has been losing his hair daily in clumps starting on the top of his head. He barely eats. I feel horrible for deciding on this shot for him. It has been two weeks and I'm trying everything to increase his appetite and energy but scared for him. Hope this information is helpful.

Replied by Stacey

Hi I saw your post, and I was wondering if you have tried Essiac Tea? Also find a good homeopathic vet who can help build up his immune system. Essiac Tea is a fantastic detox, also coconut oil and ACV are brilliant. Please also if she wont eat try syringing some food in her mouth. xx

Also to nourish her grain free food is much better than the normal cat food. Please check the meat content on the cans. x

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Posted by Joann (Atlanta, Ga) on 11/16/2011

My 5 year old cat received a feline leukemia booster yesterday. He was acting himself prior to the vaccine. I did this because I have a rescue cat which MAY be leukemia positive; because of this I have given boosters to the other cats.

This morning, I found him hiding in the closet. He is growling and not very approachable. He will not eat now. I have never seen him like this.

Because of have other cats, I have isolated him and will observe him.

I have had other cats which developed acute reactions to vaccines, including myositis, and swelling and fever. I am very concerned, because vets will assure you there are few problems, and I truly believe they think this is so in many cases; and yet read articles on the internet, and they state quite the opposite.

The truth of the matter is whenever something foreign to the body is introduced, and we really don't know what is in the vaccine, problems can happen. It is difficult to believe what the pharmaceutical companies state because this is easy money.

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Posted by Sallie (Arnold, California Usa) on 12/15/2010

For the second time, following vaccinations for Rabies and Feline Leukemia, my Siamese Cat has developed alopecia. This time it is much more serious involving almost all of her
stomach and parts of her front and back leg (on the same side)-which is on her right side. Her left side (including front and back leg) are not effected. She is beginning to lose weight too. She has been to the vet twice for this and no one has any idea what is wrong with her and state that vaccinations don't cause skin reactions - but they have twice with her. Now I

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Posted by Kyrie (Dickinson, North Dakota) on 09/29/2009

Well I got my kitten vaccinated about three weeks ago now, and she has been slowly losing the use of her back legs. It was the panleuk combo vaccine (not sure what brand) and I didn't notice it at first. She just stopped jumping around. I assumed it was because she was depressed at the loss of our other cat a short time before, as she was also sleeping more. But now? She doesn't seem to have any feeling. You can pinch the left hind leg and get no response, and the right one twitches but little else. I am not sure if this is a reaction to the vaccine but it seems too coincidental not to be considering she is an indoor only cat. If anyone has any advice please let me know!

Replied by Michelle
(Calgary, Alberta)

I went to my holistic vet and I was suggested to see a homopathic that he works with and she recommented silicea 30C homopathic medicine for 3 days 3 times a day 1 pill crushed between two spoons. It worked great! If you can check with a homopathic vet or write to Dr. Pitcarn for help.

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Posted by Jennifer (Rockville, Maryland/ USA) on 03/13/2009

my kitten has diarrhea. iv had her about a week and a half... she is six and a half months old and we adopted her from a rescue shelter... when we first got her she was fine, then about 3 days ago we took her to get her 2nd distemper and her 2nd leukemia booster and ever since she has had really bad smelling diarrhea, i was wondering if maybe it was a side effect and will it go away in like a week of so... or if it was the food i have been feeding her... the first 2 days i had her i gave her fancy feast kitten food, but then i started giving her regular fancy feast (i guess for cats) but yesterday morning i mixed a little of the kitten food with the regular food, and she eats purina kitten chow through out the day... (i leave her bowl out) do you think she is allergic to her food (hard or dry) im just unsure. thank you!


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Posted by Monica (Whittier, CA) on 02/19/2009

My 6 month old Bengal kitty received her booster vaccination yesterday along with a leukemia shot. She is a very active and playful kitten and was fine when we came home yesterday. This morning she awoke very lethargic and obviously in pain. She cried out when I picked her up even hissing, which she has never done before. She's just sitting on my bed looking at me with sad eyes. Any advice would be helpful.

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Posted by Jessi (Fairfield, IA USA) on 12/23/2008

You asked people to write and tell you if they had an experience with a side effect from a pet vaccination. My brown-and-black-striped tabby cat had problems with the leukemia vaccination. I don't remember if it started with the first vaccination or with the booster, but I believe it was with the first vaccination. What happened is, every time she got her anti-leukemia shot, she would be very ill for 3 days: TOTALLY lethargic, like a wet dishrag. After about 3 of these incidents, I said, "No more vaccinations for this cat!" She didn't respond as badly to the other vaccinations they give cats, but I decided to take her off those, too. She's an inside cat, and it was ridiculous to keep giving her vaccinations because she wasn't ever exposed to other cats. After seeing what she went through, I wouldn't give her a leukemia vac even if she were an outside cat. There was something very wrong going on inside my little girl from that shot, and I'm sorry I ever let them give it to her.

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Posted by Black Chase (Columbia, MD) on 11/15/2008

Reaction to feline leukima shot and distemper combo given at hospital. My very healthy cat (temp 99)went to Banneker for an annual on his 1 year birthday. By Am he hide under the bed, screamed in pain if touched and had a stinky dry mouth. His temperture was at 104.4. What do you thin happened? They claim he diveloped a urinary infection. Any ideas?

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Posted by Vicky (Falmouth, Maine) on 04/06/2008

I had all three of our cats vaccinated in January for rabies and feline leukemia. Even though all are inside cats, I thought it best to vaccinate against feline leukemia because they were going on a plane to Florida with my sisters cat, who is an outside cat and I thought he might carry the virus. What a terrible mistake. Within a few hours, all three of my cats were weak, lethargic amd breathing very shallowly. I called the vet and they said that this is a normal reaction and to watch them. The oldest cat, a nine year old persian, was the worst. Her eyes leaked out a brown color liquid. The other two, a 6 month old male and a two year old female did a little better, but they didn't eat for at least 24 hours. It was a terrible scare, but this isn't over as yet. Our beautiful young male manx mix (Mickey) got very sick 10 days later. I took him to the emergency vet after he vomited repeatedly, was disoriented and had a fever of 105. The vet gave him a shot of anti-biotic and liquids and sent me home with (baytrill) antibiotic for 10 days. My vet said to bring him in if he exhibits any more signs of illness. Approximately 2 weeks after the antibiotic was finished my cat became very ill again. This time the emergency vet took an xray and my cat had pneumonia. The emer. vet gave me two weeks of antibiotic and told me to make sure to take him to my own vet after the antibiotic is finished. I just took him back and my vet put him on another week of antibiotic and then he will xray him to see if his lungs are clear. It goes without saying that I really think that this was caused by the rabies and feline leukemia shot given all at the same time. I feel so stupid for doing this, but I didn't know that an animal can get so sick from vaccinations. I know now. I won't be giving my beautiful cats any more shots. Please pray for my Mickey...

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Posted by Carmen (Silver Spring , MD) on 03/27/2008

My cat (4 years, female, indoor-outdoor) got three days ago her distemper shot( renewed after 3 years) and for the first time the feline leukemia vaccination. Hours later she appeard tired, apathic, lack of appetite, desinterested and had a feaver. The vet gave her then shots of benadryl and steroids. Within hours she was better. But after another 24 hours she is now again tired, no appetite, hiding under beds, desinterested. I am veryconcerned. I am going back to the vet tonight.