Cat Vaccine Reactions: Normal Side Effects and Signs That Need a Vet

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

Vaccines save lives, and serious reactions are rare. Even so, it helps to know what is normal, what is not and what to do. Being prepared lets you protect your cat's health without anxiety.

Why cats are vaccinated

Core vaccines protect against deadly or highly contagious diseases such as panleukopenia, calicivirus, herpesvirus and rabies. Others, such as FeLV, depend on lifestyle. See cat vaccination schedule, feline panleukopenia and rabies and cats. The benefits far outweigh the small risks for most cats.

Common, mild reactions

These usually appear within a day and last up to two days:

• Tiredness, and sleeping more.
• Slightly reduced appetite.
• Mild fever, with a feeling of being unwell.
• Soreness, and a small lump at the injection site.
• Mild sneezing after intranasal vaccines.

Give your cat a quiet, comfortable place, and watch. Do not give human painkillers. See cat poisoning: what to do.

Reactions that need prompt care

• Vomiting or diarrhea.
• Facial swelling, especially around the eyes and muzzle.
• Hives, or intense itching.
• Persistent lethargy beyond two days.
• A lump that gets larger, painful or hot.
• Limping, if the vaccine was in the leg.

Call your vet.

Emergency: anaphylaxis

A severe allergic reaction typically occurs within minutes to a few hours. Signs include trouble breathing, collapse, pale gums, rapid heartbeat, vomiting and swelling. Go to an emergency clinic immediately. Treatment includes injections of epinephrine, steroids and antihistamines, oxygen and fluids. See cat emergency warning signs. Tell your vet about any past reaction, so that the plan can be changed, such as using different products, spreading vaccines out or staying at the clinic for observation.

Injection site lumps

A small, firm lump at the site can appear a few weeks after vaccination, as part of the immune response, and usually shrinks within a few weeks. But a lump that lasts more than three months, is larger than 2 centimeters or is growing needs to be checked, since a rare tumor called an injection site sarcoma may develop. See injection site sarcoma in cats.

Reducing risk

• Follow a tailored schedule, since not every cat needs every vaccine every year. Many adult cats get core vaccines every three years.
• Give vaccines in recommended sites, such as low on the limbs or tail, where a tumor could be removed.
• Record the product, date and site.
• Monitor lumps.
• Tell your vet of any illness before vaccination, since sick cats should wait.
• Keep your cat at the clinic for a short while after vaccines, if you have concerns.

Kittens

Kittens receive a series. Mild effects are common. See kitten first vet visit.

Seniors

Older, indoor cats may need fewer vaccines. Ask your vet. See senior cat care guide.

Preparing for a vaccine visit

Bring your cat's vaccination records, and mention any past reactions, current illnesses or medications. Ask which vaccines are being given, and why. Ask about the injection site, and whether it will be recorded. Plan to stay home with your cat that evening, so you can watch it. Keep the clinic number handy. Choose an appointment time that allows you to reach the clinic if needed.

Tracking and recording

Take a photo of the injection site on the day, and check it weekly for the first month. A small, firm lump is common, and should shrink. Write down the date, vaccine and site in your phone. This simple habit is the best way to follow the 3-2-1 rule if a lump does appear. See injection site sarcoma in cats.

Cats with previous reactions

If your cat has had a reaction, your vet may suggest pre-treatment with an antihistamine, giving vaccines on separate days, using a different brand, or testing antibody levels, called titers, to decide whether a booster is needed. Never skip rabies vaccination if the law requires it, but your vet may be able to arrange an exemption if the cat's health is at risk.

Vaccine timing and illness

Do not vaccinate a cat that is sick, unless the vet decides it is worth it. Postpone vaccines in a cat with fever, vomiting or poor appetite. Tell the vet about all signs in the days before the visit.

Questions to ask

Ask whether each vaccine is needed, given your cat's lifestyle, how long each lasts and what the common side effects are. A good vet will explain and tailor the plan. See cat vaccination schedule.

When to see a vet

See a vet if your cat has facial swelling, vomiting or lethargy after a vaccine. Use the US vet directory to find a clinic.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.