Cat Vaccination Side Effects: What's Normal and What's Not

Normal reactions (no action needed)

These are signs of your cat's immune system responding to the vaccine — which is exactly what should happen.

Mild lethargy (12–24 hours)

Your cat may be quieter than usual for the rest of the day after vaccination. They may sleep more, play less, and generally seem "off." This is the most common reaction and resolves completely within 24 hours. If lethargy persists beyond 48 hours, call us.

Slight soreness at the injection site

Your cat may flinch or pull away when touched near the injection site. This is similar to the arm soreness humans feel after a flu shot. It typically resolves within 24–48 hours. Avoid pressing or rubbing the area.

Reduced appetite (one meal)

Some cats skip one meal after vaccination. This is normal. If your cat refuses food for more than 24 hours after vaccination, call us.

Mild, transient fever

A slight temperature increase is a normal immune response. You may not even notice it — cats with mild post-vaccination fever simply seem a little quieter and warmer to the touch. It resolves on its own.

A small, firm lump at the injection site

A pea-sized lump at the injection site can develop within the first few days. This is a localised immune response and usually resolves within 2–4 weeks. If the lump persists beyond 4 weeks, grows larger than 2 cm, or appears more than 4 weeks after vaccination — contact us immediately. This is rare but important (see FISS below).

Uncommon reactions (monitor and call if concerned)

Swelling at the injection site persisting beyond 48 hours

A small amount of swelling on the day of vaccination is normal. Swelling that increases or persists beyond 48 hours should be evaluated. Call us to discuss — it may warrant an in-person check.

Vomiting or diarrhoea

Occasional vomiting or loose stool within 24 hours of vaccination can occur. It's usually self-limiting. If vomiting occurs more than twice or diarrhoea persists beyond 24 hours, call us.

Sneezing (after intranasal vaccines)

If your cat received an intranasal vaccine (which is less common than injectable vaccines), mild sneezing for 2–3 days is a normal local reaction. This doesn't mean your cat is sick — it's the vaccine working at the site of administration.

Mild facial swelling or hives

This is an allergic reaction — uncommon but not dangerous if addressed promptly. If you notice swelling around the eyes, lips, or ears, or if raised bumps (hives) appear on the skin, call us the same day. We may administer an antihistamine.

Rare and serious reactions

Anaphylaxis

What it is: A severe, systemic allergic reaction occurring within minutes of vaccination.

Signs: difficulty breathing, sudden collapse, vomiting, diarrhoea, facial swelling, pale gums, rapid heart rate.

How rare: Extremely rare — estimated at less than 1 in 10,000 vaccinations.

Why we ask you to wait: At Pawspact, we ask every client to remain at the clinic for 15–20 minutes after vaccination. If anaphylaxis occurs, it almost always happens within this window — and we have the equipment and medications to treat it immediately. This is why vaccination should always be performed at a veterinary clinic, not at home.

Feline Injection-Site Sarcoma (FISS)

What it is: A rare type of tumour that can develop at the site of a previous injection — not only vaccines but any injectable medication or substance.

How rare: Approximately 1 in 10,000 to 1 in 30,000 vaccinations. The risk is very small but real.

What to watch for (the 3-2-1 rule):

• The lump is still present 3 months after vaccination
• The lump is larger than 2 centimetres
• The lump is still growing 1 month after vaccination

If any of these apply, contact us promptly. Early detection and treatment of FISS significantly improves outcomes.

What we do to minimise risk:

• We follow WSAVA guidelines on vaccination frequency — no unnecessary vaccines
• We use specific injection sites recommended by veterinary oncology guidelines (limbs rather than the interscapular region) so that if a sarcoma develops, surgical options are maximised
• We record the exact injection site in your cat's medical record at every visit

What to do after your cat's vaccination

First 24 hours

• Keep your cat calm and comfortable in familiar surroundings
• Offer fresh water and food as normal — don't worry if they skip one meal
• Monitor the injection site for excessive swelling
• Observe their behaviour — mild quietness is fine; complete unresponsiveness is not

When to call us

• Lethargy lasting more than 48 hours
• Refusal to eat for more than 24 hours
• Vomiting more than twice
• Difficulty breathing (emergency — call immediately)
• Severe facial swelling (call same day)
• A lump at the injection site that persists beyond 4 weeks or grows beyond 2 cm

When to call 999 or come to the clinic immediately

• Collapse or inability to stand
• Difficulty breathing
• Severe swelling of the face or throat
• Seizures

These are signs of anaphylaxis and require immediate veterinary attention.

Do the benefits outweigh the risks?

Overwhelmingly yes. The diseases that vaccines prevent — panleukopenia, rabies, feline leukaemia — are far more dangerous than any vaccine side effect.

The mathematics are clear. Vaccination is one of the safest and most effective medical interventions available for cats. The rare risks are manageable. The risks of non-vaccination are not.

What if my cat has had a reaction before?

A previous reaction doesn't necessarily mean your cat can never be vaccinated again. It means the next vaccination needs to be managed more carefully.

At Pawspact, if your cat has a history of vaccine reactions, we may:

• Pre-medicate with antihistamines or anti-inflammatory medication
• Use a different vaccine brand or formulation — reactions can be formulation-specific
• Extend the observation period after vaccination
• Adjust the vaccination schedule — spacing out vaccines that were previously given together
• In very rare cases, consider titre testing as an alternative to re-vaccination for certain core vaccines

The decision is always individualised. We discuss the options with you, explain the risk-benefit balance, and make the decision together.

Your cat's safety is part of the pact

At Pawspact, we take vaccine safety seriously — from selecting the right formulations, to recording injection sites, to following evidence-based schedules that avoid unnecessary doses. We want your cat protected. We also want them safe.

Book a vaccination appointment →
Call: 02 674 7484
WhatsApp: 02 622 7260

For the full vaccination picture: Cat Vaccinations in the UAE: A Vet's Complete Guide.