How To Recognize A Cat's Normal Versus Abnormal Side Effects After A Vaccine

Posted on: 20 January 2016

If you're preparing to take your cat in for their first vaccinations, you should know that there may be some mild side effects. Cats, like people, sometimes feel a little under the weather after being given a vaccination. However, it's important to be able to discern the difference between normal, mild side effects and abnormal side effects that may be serious warning signs. This guide will easily explain the difference between the two, and what you should do if your cat is experiencing the latter.

Normal Side Effects

The minor side effects a cat may normally experience after a vaccination are nothing in comparison to them actually catching the disease they're being vaccinated for. Even so, however, a cat may exhibit these signs during the day they were vaccinated, or for a bit longer:

  • Lethargy - Cats who have been recently vaccinated may seem tired and uninterested in play or exploration. This is completely normal, and is quite similar to how you might feel after a flu shot.
  • Minor Cold Symptoms - Cats may exhibit slight cold symptoms for a brief period after being vaccinated, since a dead virus has been introduced into their body. The body goes to work developing antibodies for this disease, which may cause slight symptoms like sneezing, coughing, or a minor elevation in temperature.
  • Lack of Appetite - This is another common symptom, but it shouldn't go on too long. Make sure your cat is drinking regularly and regains their appetite by the next day at the latest, or they may need medical attention.  

‚ÄčAbnormal Side Effects

While it's extremely rare, some cats may experience allergic reactions or sensitivities to the vaccines they're given. In these cases, your cat may experience swelling at the injection site. Veterinarians and technicians tend to inject only one vaccine per leg so that they can easily determine which vaccine has set off your cat. If one of your cat's legs is swelling or developing a lump, call your vet right away.


Depending on the severity of the swelling or bump, your veterinarian may either suggest that you wait to see if it goes down, or come in immediately. If they ask you to come in, they'll examine the swelling, and possibly prescribe a steroid to reduce the immune system's overreaction to the vaccine. If your vet suggests that you wait and see, you can help to ease your pet's discomfort and reduce the swelling by putting a cold pack on the injection site.

Vaccines save lives, and the likelihood of your cat having any kind of serious reaction is extremely minimal. However, knowing the difference between a normal reaction and a serious one can help you to protect your cat, just in case. Click here for more information on cat vaccinations.