Lump Under Cat’s Skin After Vaccination

Vaccinations are a necessary part of pet ownership and have saved countless lives. But like any medical treatment, they come with their risks.

Is it normal for a cat to develop a lump under the skin after a vaccination?

The short answer is yes, a small, mobile, firm, painless lump at the injection site can develop granuloma that is comprised of a collection of immune cells. In most cases, this lump will go away within a few weeks. Warm compresses can be of help.

A far more serious side effect is a vaccine-associated sarcoma (VAS), which is a rare but aggressive type of cancer of the connective and soft tissues. It is most often associated with rabies and feline leukemia vaccines. The incidence is between 1 – 1,000 to 1 – 10,000 cats.

What should you do if you notice a lump under a cat’s skin?

Keep a close eye on it. If the lump hasn’t disappeared within a month or if the lump grows larger, seek veterinary attention.

Veterinarians have created the 3, 2, 1 rule in deciding how to test for a lump after vaccinations.

3: Present in any form for three months after vaccination

2: Larger or equal to 2 cm across (Dr Sue, Cancer Vet recommends any lump larger than the size of a pea which has been there for a month be investigated)

1: Present for one month after vaccination and fast-growing

In any of the above cases, the veterinarian will perform a wedge biopsy of the lump for microscopic evaluation.

Other vaccination side-effects

Typically, side effects are self-limiting but may include general malaise, loss of appetite, low-grade fever, sneezing and pain at the site of the injection. These usually only last a day or two. If symptoms persist, please take your cat back to the veterinarian.

Vaccine protocol

The Vaccine-Associated Feline Sarcoma Taskforce now recommends that veterinarians now administer vaccinations in different locations on your cat’s body. Current protocols are:

  • Rabies – Right rear leg
  • Feline leukemia – Left rear leg
  • FRVCP (F3) – Shoulder

The reason for this is if a cat develops VAS, it is easier to remove the entire limb.

Annual vs tri-annual boosters

A great number of veterinarians are switching away from the annual booster in preference of booster shots every three years, for low-risk cats. Speak to your own veterinarian as they know your cat, his medical history and the incidence of diseases in your area.

Many local councils require an annual rabies vaccine, and you must comply with these regulations. Only high-risk cats such as ones who free roam should receive the feline leukemia vaccine.

Please remember that vaccines have done far more good than harm. Being aware of any lumps and bumps, following your veterinarian’s vaccine protocol and seeking medical attention quickly is the best course of action.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio

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