Is My Cat's Lethargy an Allergic Reaction?

A once playful kitten looses all energy after a routine vaccination.

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Cat Expert Dr. Plotnick

Dear Dr. Plotnick,

I took my 2-year-old Siamese cat to the vet for his annual check-up. During the exam, he received his booster distemper shot. He has only been to the vet for his kitten shots and his neuter operation. About an hour after we bought him home, he started licking himself. Every time he licked a spot on the underside of his tail, about 2 inches from his anus, he became itchy, licked and bit at other spots on his body and ran away.
The rest of the night he was quiet, or he licked other spots and was fine. But as soon as he licked the spot on his tail, he ran away and hid. The next morning, I called the veterinarians office and they said it may be a reaction to the distemper vaccination. (He has had this shot as required as a kitten and never had any reaction.) They told us to give him a half of a 4 mg pill of Chlortrimeton, antihistamine, three times a day. We did this and it seemed to help the itching or hypersensitivity in the tail and he doesn't lick and bite anymore. However, he has lost all his energy; he is completely lethargic when before he was a playful and active cat.

Could this be a side effect of the vaccine? We haven't given him any more Chlortrimeton because we thought that may be affecting his behavior. (The itching isn't as bad). Or could he be upset about the vet visit experience?

-- Marie and Ed

Dear Marie and Ed,

The fact that this unusual licking behavior started about an hour after he received his vaccination certainly suggests that this is a reaction to the vaccine. Occasionally a vaccine will trigger an allergic reaction that can cause cats to itch. These reactions often diminish eventually; however, antihistamines usually accelerate the resolution of the clinical signs. In my experience, Benadryl is more effective for this than Chlortrimeton; however, both drugs are appropriate for this kind of reaction.

A more common adverse reaction to a vaccine would be lethargy, the kind that you're describing. This usually resolves with no treatment after 24 or 48 hours, although occasionally a cat might require a little supportive care (force feeding, subcutaneous fluids) during this time. You didn't mention in your letter how long this lethargic period has lasted. If it has been longer than 48 hours, then I suspect that this is not because of the vaccination. Whether theres an underlying illness or at 2 years old, your cats extended kittenhood has finally ended and he's a quieter, more mature cat now is difficult to say.

Arnold Plotnick, DVM

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Reader Comments

Kevin    Gatineau, QC

12/28/2009 10:33:52 PM

My 1-year old cat was vaccinated 5 weeks ago. He had no health problems prior to the vaccination. Within an hour of his vaccination he began biting the area of injection. He was never a cat to groom himself, but now I cannot get him to stop licking. He's licking right now as I type this. Sometimes he jumps and runs to the basement like he's on fire. He's an indoor cat and it's winter here - no fleas or bugs. Whatever was in the vaccine did a number on him. I showed a video clip to the vet and he agreed the vaccine caused this behavior. He put the cat on prednisone. He's finished it as of yesterday, but he still has some inflammation in his joints, is lethargic, is constantly licking, has low appetite, does not want to play, and is not as affectionate as he used to be. It breaks my heart to see him this way. I advise people with indoor cats to forget about the vaccinations. This cat will never get one again. I hope he survives this!

christina    El Cajon, CA

6/8/2009 12:50:30 PM

I am getting ready to have both my cats get their distemper shots even though they are indoor cats because i care for 24 feral cats at another facility and one may have died of feline distemper. and because i handle the dishes of the feral cats i don't want to chance getting my house cats sick. but after reading this acticle and what others are saying about allergic reactions i am torn about getting my 2 cats shots. Both of my cats already have allergies and can't afford any other problems.

Jason    Grayslake, IL

1/13/2009 7:29:58 PM

We took my 8 year old cat to have his distemper shot this past weekend. Within 24 hours after the shot, he became lethargic and started vomiting. He wouldn't eat for 2 days and the vomiting continued on occasion during that timeframe as well. We ended up having to bring him back to the vet and they inserted a IV cathidor and gave him fluids because he was so dehdrated. He had a episode very similar to this over the summer and after looking at our records, we noticed it occured the day after his brother had his distemper shot administered. I know this sounds strange, but is it possible a cat can have a reaction to a distemper shot that was given to another cat? I know he licks his brother all the time so it makes me wonder.

Jennifer    Lubbock, TX

10/26/2008 11:09:44 PM

Not exactly the info I was looking for, but got other info that was helpful in my search for answers. Thank you for the help!

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