Why Is My Cat Lethargic After Shots? 

Dr. Joe Alcorn, M.S., D.V.M.

Dr. Joe Alcorn is founder of Care Animal Hospital in Temecula, California. He has a Bachelor of Science in Biology and Doctor of Veterinary Medicine from Colorado State University. He is a member of the American Veterinary Medical Association and his advice has been featured in large publications like Bustle and Martha Stewart.

Home » Blog » Why Is My Cat Lethargic After Shots? 

When cat owners ask me, “Why is my cat lethargic after shots?” I typically tell them that it’s normal for cats to feel unwell after vaccines. However, it’s important for cat owners to not overlook potentially serious reactions and mistake them for post-vaccine lethargy. This article outlines the plausible causes for lethargy and how to care for your pet during this time.

Why Is My Cat Lethargic After Shots?

Most cats experience some level of lethargy after getting shots, mainly due to a cat’s immune system responding to the vaccine. Soreness or localized swelling at the vaccination site and potential sedative effects are also other factors that may cause them to be lethargic. In rare instances, an allergic reaction called anaphylaxis can also cause extreme lethargy in cats.

Yellow tabby cat yawning while sitting on a bed

These are normal reactions that last for a day or two. Understanding how vaccines work and their side effects can help you provide the best aftercare for your pet.

ReasonSide Effects
Immune system responseFatigue, mild fever, decreased appetite
Soreness or localized swellingDisinterest, pain response to touch, infection
Medication side effectsDrowsiness, fatigue, irritation
AnaphylaxisExtreme weakness, collapse, difficulty breathing

Reasons Why Cats Feel Tired After Shots

Cats may feel tired after vaccines because the shots release antibodies to fight off potential diseases, triggering a mild fever. An upset stomach, soreness, and cold-like symptoms can make cats feel quite exhausted. To avoid unnecessary worry and stress, here are some reasons why your feline friend feels tired after a vaccination visit to the vet:

1. Immune System Response

There are different types of vaccines that are used for pets. According to the MSD Manual, “A vaccine may contain either living or killed organisms or purified antigens from these organisms.” When your cat gets a shot, the immune system responds by releasing antibodies for a particular infectious organism.

Pet vaccinations stimulate an animal’s immune response to help cells circulate in the body. When your cat is exposed to a bacteria or virus, your pet’s body is ready to fight it. The process can consume more energy than usual, making cats tired and sleepy.

Most of the side effects of cat immunization are mild and shouldn’t last long. However, you must still observe these potential side effects.

2. Soreness or Localized Swelling

Soreness in the vaccination site is among immunization’s most common side effects. Your cat may feel extra protective of its body due to soreness. That’s why after administering the shot, I immediately explain to owners that cats may not feel like exercising or playing outdoors after getting a shot.

Assistant holding onto a black and gray cat while a veterinarian is holding a syringe

When there’s a sore body part, your cat’s body responds to slight pain, making them feel tired. While this soreness shouldn’t last long, bring your cat to my clinic if the lump grows, shows signs of infection, or doesn’t disappear within a week.

3. Medication Side Effects

Your cat’s body will consume energy due to an inflammatory immune response of releasing antibodies. Mild symptoms, including tiredness, an upset stomach, and cold-like symptoms, are entirely normal.

  • Sleepiness: About 40% of adult cats can sleep up to 18 hours a day, more when they’re not feeling well. Like humans, cats may feel tired and a little sleepy after getting a shot. Some veterinarians also provide a mild sedative to anxious cats, and this sedative increases drowsiness.
  • Sneezing: Most vaccines are administered through injections. However, some vaccines are available as drops or sprays. Intranasal vaccine side effects can resemble cold-like symptoms, including sneezing, coughing, and runny nose.
  • Upset stomach: Your cat may also experience a decreased appetite within 24-48 hours after vaccination. They may have a mildly upset stomach, also causing them to feel lethargic. Cats tend to withdraw when they have an upset stomach. 
  • Slight fever: A vaccine triggers fever in cats by introducing weakened or inactivated forms of the disease. This prompts a cat’s body to respond like it’s fighting a real infection. The inflammatory response raises body temperature, resulting in a mild fever that may last within a day or two.

4. Anaphylaxis

Severe anaphylaxis reactions can show within 48 hours after getting the shot. This is the most severe allergic reaction your cat can get from immunization.

In rare cases, cats may have allergic reactions to modern vaccines, leading to extreme weakness, hives, nausea, and collapse. Contact my clinic immediately for emergency care and services if you notice difficulty breathing, vomiting, excessive drooling, and diarrhea a few hours after the vaccination.

Cat lying on a bed

The Effects of Vaccines On a Cat’s Immune System

Vaccines are designed to simulate an immune response by introducing a weakened or inactive form of a virus into the body. This prompts an immune response of recognizing the foreign antigen and producing specific antibodies to combat it. 

The vaccine triggers this response in a controlled manner. In effect, your cat’s body will defend itself faster when exposed to actual viruses in the future.

A study shows that vaccine-associated adverse events only have a low rate of 0.52% within 30 days of vaccination. While side effects can occur, cats can generally fight these off after one to two days.

Lethargy After Vaccinations

Pet immunization is a process that introduces a foreign antigen in their bodies. It triggers an inflammatory immune response that increases the body temperature as a defense mechanism to kill off potential pathogens.

Although this results in an unpleasant feeling, a tired cat after vaccination signals that its body has effectively responded to the vaccine.

Limping After Vaccinations

Injecting vaccines into the loose skin around a cat’s neck or scruff is typically easier and less painful. Certain feline vaccinations have been linked to an aggressive form of cancer called feline injection site sarcomas (FISS). FISS has a low rate of incident risk annually, with prevalence occurring only in 1 in 10,000 cats.

Some veterinarians now administer the shots as low as possible on the rear limb of cats. A cat’s body directs inflammatory cells to the injection site after vaccination, which is why some cats may limp.

This localized inflammatory response can sometimes manifest as tenderness, pain, or a firm lump developing over days or weeks near the injection area.

White and gray cat sleeping on its back with its paws up

Should I Vaccinate My Cat Despite Side Effects?

I recommend vaccinating your cat despite side effects and even if they feel tired afterward. As a pet owner, you are responsible for your pet’s well-being, and getting them vaccinated on time can protect your feline friend’s long-term health.

By keeping your cat up-to-date on core vaccines, you are safeguarding them against deadly yet preventable diseases. The high efficacy and relatively minimal risks of side effects make vaccination well worth protecting your feline’s long-term health.

  • Vaccines protect against fatal diseases: While the feline panleukopenia virus has a 90% mortality rate in untreated cases, vaccination provides immunity.
  • Vaccine effects are mild: Serious adverse reactions are rare, with minor lethargy and decreased appetite disappearing one to two days post-vaccine. 
  • Vaccines prevent the spread of disease: Vaccinating your cat allows their body to protect itself from diseases while also taking part in preventing outbreaks.

What Are Ways to Help My Cat Recover After Getting Shots?

Cats feel tired after getting vaccinated because their body does a lot of work releasing antibodies to fight off bacteria. This process can make them drowsy and experience soreness, cold-like symptoms, and even an upset stomach.

Here are some things you can do to make your cat feel better after immunization:

  1. Provide a quiet place to rest: Your cat will most likely want to sleep after their vaccine appointment. Make sure they have a place to rest comfortably, away from noises or commotion.
  2. Give plenty of fluids: Make sure your pet has access to fresh, clean water to avoid dehydration.
  3. Monitor appetite: While your cat may lose their appetite right after getting a shot, you must still encourage your pet to eat at their usual time.
  4. Avoid playing: Your pet may feel soreness in the injection site for a few hours. If you have other pets, try to keep your cat isolated from them for a while to limit their activity. 
  5. Give some alone time: After a vaccination appointment, your cat may not feel like socializing or cuddling with you. It would be best not to force them to do so either. Just let them be on their own as they recover their energy.
  6. Check temperature: Cats have an average body temperature of 100 to 102.5 degrees Fahrenheit. A temperature above 103 degrees Fahrenheit can be too hot for your cat to handle. If this happens, connect with a vet immediately.
Veterinarian administering vaccine to a cat

A report shows that only 61% of cat owners secured core vaccinations for their pets. One reason for such reluctance is fear of side effects, including cold-related ones. Pet owners must remember these vaccinations are for the long-term well-being of their pets. With these aftercare tips, your cat will regain their strength and be back to their normal selves in no time.

Related Questions

Do Cats Feel Unwell After Vaccinations? 

Cats can feel unwell and lethargic for one to two days after vaccinations. This is due to the immune system’s response in producing antibodies to fight against the infectious diseases introduced by the vaccines.

How to Make a Cat Feel Better After Vaccines?

To help a cat feel better after vaccines, provide a quiet resting space away from noise and activity. Let them have access to fresh water and try encouraging them to eat even if their appetite is decreased.

How Can You Tell if a Cat Has a Fever?

To check if a cat has a fever after vaccines or due to other infectious diseases, feel their ears and use a thermometer rectally or under their arm. A temperature over 103 degrees Fahrenheit indicates a concerning fever that may require veterinary attention.

How Can I Prevent My Cat From Having Allergic Reactions to Vaccines?

To prevent your cat from allergic reactions to vaccines, vets can administer the shots for your cat at different times or even weeks apart instead of giving multiple vaccines at once. Depending on your pet’s health, I also recommend skipping certain vaccines until your cat’s body is ready.

How Long Do Cat Vaccine Side Effects Last?

Minor side effects of cat vaccines should last around 24 to 48 hours, while major ones may go beyond two days. It would be wise to bring your pet to my clinic for examinations if the effects make your cat extremely uncomfortable.


Vaccines help maintain your cat’s health and well-being. While sleepiness, soreness, and cold-like symptoms are typical side effects, you can still visit my vet clinic to address serious allergic reactions caused by vaccines. With proper care, not only will your cat get their energy back quickly, they will also live long, healthy, disease-free lives.