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Why is my cat still sick and lethargic 3 weeks after his vaccine?

Updated On September 23rd, 2025

Pet's info: Cat | Mixed Breed | Male | unneutered | 8.25 lbs

According to my vet my cat has had a reaction to the leukemia vaccination. It's been three weeks, very little poop, very lethargic, not playful. He is three. This was his first ever shots. He will eat canned food with pumpkin. He is peeing. How long does it take for him to feel better? I should note they treated him at the same time with topical flea treatment. I went back 4 days ago and they looked at him and said increase the wet food. Not helping any.

2 Answers

Most Helpful Answer

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Answered By Dr. Leigh, DVM

Veterinarian

Published on September 28th, 2017

That is very unusual that he is not better and I think he should have a work up to try to figure out the cause. Your vet can run some bloodwork to rule out potential medical problems. Most cats are usually better within a few days after having a reaction to a vaccine and three weeks seems like a very long time. If your vet can't do a work-up then you should go to a different vet for a second opinion and work-up. So sorry that he is having this problem.

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Other Answers

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    Answered By Susan England-Foster

    Veterinarian

    Published on July 14th, 2017

    If she had a vaccine reaction to the feline leukemia vaccine it should of resolved by now. Usually vaccine reactions start with in minutes to hours after vaccines. If severe patients might need steroids and supportive care. I would recommend taking him to a veterinarian for a full exam. It is possible he has a viral, bacterial or fungal infection that needs medical care.

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