Virtually all cats will be exposed to the highly contagious virus that causes feline distemper at least once.

Feline distemper is a highly contagious viral disease that is especially harmful to young kittens, who can die without warning from the infection. Because the virus that causes distemper is so widespread in the environment, the distemper vaccine is recommended for all cats—even those who only live indoors. And it’s particularly important to protect young kittens as soon as it’s safe to do so, as they’re the most vulnerable to serious illness. 

What Is Feline Distemper?

Feline distemper (also called feline panleukopenia, feline infectious enteritis, and feline parvo) is a disease caused by the feline panleukopenia virus. According to the American Veterinary Medical Association (AVMA), the virus kills rapidly growing and dividing cells in the body, like those found in the bone marrow, lymph nodes, intestinal lining, and developing fetuses. 

How Do Cats Get Distemper?

The AVMA says infected cats release the feline panleukopenia virus in their urine, poop, and nasal secretions. Unvaccinated cats who come in contact with these substances—either directly or through an object harboring the virus, such as bedding, food bowls, litter boxes, and the hands and clothing of people who’ve interacted with infected cats—can become infected with the virus. It can also be spread from a pregnant cat to her developing fetus via the placenta. 

Unfortunately, the virus is particularly difficult to get rid of and can survive in the environment for up to a year. As a result, virtually all cats and kittens are exposed to it at some point in their lives. People, however, are not at risk of infection.

What Are Signs & Symptoms of Distemper in Cats?

The Merck Veterinary Manual explains that most infected cats don’t show any signs. Cats can become infected at any age, but cats under the age of one are most likely to become severely sick, and kittens under the age of five months are most at risk of dying from the infection. Sadly, death can occur without warning.

  • Fever
  • Lethargy
  • Loss of appetite
  • Vomiting
  • Diarrhea
  • Dehydration
  • Low white blood cell count (called leukopenia—where the virus gets its name).

In addition, if an infected pregnant cat passes the virus to her growing fetus, the fetus may die or suffer serious brain damage. 

When Should I Vaccinate My Cat for Distemper?

Trent Eddy, DVM, of Ironhorse Veterinary Care in Leawood, Kan., says the feline distemper vaccine is considered to be a core vaccine, meaning it’s recommended for every cat, regardless of whether they live indoors or outdoors. The distemper vaccine makes this important list because of how common the virus is the environment. According to the AVMA, it’s “virtually everywhere.” 

Eddy explains that the vaccine for distemper is typically delivered in a three-in-one combination vaccine (called the FVRCP vaccine) that includes two other core vaccines: one for feline viral rhinotracheitis, and one for feline calicivirus. The AVMA says most kittens are vaccinated between the ages of six and eight weeks and receive follow-up vaccines until they’re 16 weeks old. If you have an adult cat, the proper time to vaccinate depends on variables like her age, health, and risk of infection.

You’ll need to visit with your veterinarian about your particular cat’s specific vaccine schedule—especially if you have a new kitten. Kittens are most susceptible to serious illness and death from distemper. 

cat getting a shot from veterinarian
Credit: Tomwang112 / Getty

What Are the Side Effects of the Distemper Vaccine?

The most common side effect Eddy sees after vaccinating cats is general lethargy the day of and the day after, but that can actually be a good thing. “Lethargy is typically a positive sign because it means the body is really being stimulated to make antibodies against the disease-causing organism,” he explains. 

While lethargy and even soreness at the injection site (much like you might feel after a flu shot) aren’t a cause of concern, allergic reactions are. “They can happen with any cat, any age, and any vaccine,” Eddy says. Luckily, such reactions to the distemper vaccine are rare. In 15 years of practice, Eddy has only seen adverse vaccine reactions to any vaccine in a handful of patients. He says they typically appear almost immediately, while the cat is still in his care. 

Signs of a mild allergic reaction include mild fever, itchiness, and swelling and redness of the eyes, lips, and neck. In more severe cases, vomiting, diarrhea, and breathing problems can occur. (Some cats may even collapse.) If your cat starts showing any of these signs within hours of being vaccinated, call your veterinarian as soon as possible. 

Another rare but serious vaccine reaction is the development of a tumor at the site of injection. While mild swelling at the injection site is normal in the few days following a vaccine, swelling that grows or doesn’t go away after three weeks is cause for concern as it could be a sign your cat has an injection-site sarcoma. These cancerous tumors can form weeks, months, and even years after the vaccine was given. If you notice such a lump under your cat’s skin, call your vet right away. 

Should My Cat Get the Distemper Vaccine?

No vaccine (or medical treatment, for that matter) is completely without risk. If you aren’t sure about vaccinating your cat, talk to your vet. They are in the best position to help you weigh the risks of vaccinating versus not vaccinating your cat.