Lethargic, feverish cat after vaccination: what to do
1-year-old cat vaccinated yesterday against panleukopenia, herpesvirus, calicivirus and FeLV. Today it is lethargic, eating less and has a temperature of 39.6 °C. Mucous membranes, pulse and breathing are normal; no oedema or vomiting.
What is the most appropriate course of action?
chevron_right Show answer and explanation
A. A broad-spectrum antibiotic in case the fever is an injection-site infection
A mild fever within 24–48 hours of vaccination is an expected inflammatory response, not an infection; antibiotics are not indicated.
B. Monitoring and supportive care if needed, record the batch in the clinical record and report the suspected reaction to the veterinary pharmacovigilance system
Correct. This is the most common adverse reaction and usually resolves within 1–2 days. Even mild suspected reactions should be reported to the Spanish Medicines Agency (AEMPS) veterinary pharmacovigilance system: that is how batch or product problems are detected.
C. Contraindicate all future vaccination
A mild, transient reaction does not contraindicate vaccination: assess which vaccines are essential, consider splitting them across visits and monitor the cat after each one.
D. Revaccinate in 2 weeks, because the fever shows the vaccine has not worked
Fever does not indicate vaccine failure; it reflects immune activation. Repeating the dose for no reason only adds risk.
lightbulb Key takeaway
Distinguish a mild reaction (lethargy, fever, local pain) from anaphylaxis, which in cats usually causes respiratory and gastrointestinal signs within minutes. Always record the product, batch and injection site of each vaccine.
References: WSAVA Vaccination Guidelines 2024
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.