Cat flu is a general term for upper respiratory disease in cats caused primarily by feline herpesvirus (FHV-1) and feline calicivirus (FCV). Signs include sneezing, nasal and eye discharge, fever, and mouth ulcers. It is not related to human influenza. Most cases resolve with supportive care, but severe FCV and FHV-1 in kittens or immunocompromised cats can be life-threatening. Both viruses are covered by the core vaccination schedule — see our cat vaccinations guide .

Can a vaccinated cat still catch cat flu?

Yes, but the disease is typically milder. Vaccines do not provide sterilising immunity against FHV-1 and FCV — a vaccinated cat can still become infected but is much less likely to develop severe disease. FCV in particular has many strains; vaccines cover the most common but cannot protect against all variants. This is why booster schedules matter: older vaccines may not cover newer circulating strains.

I just adopted a cat from a shelter. Should I be concerned?

Any newly adopted cat — particularly from a high-density shelter environment — should see a vet within 48–72 hours of coming home. Check vaccination history and keep the new cat isolated from resident pets for at least 7 days. Our first week home guide covers isolation protocol, and our cat introduction guide explains the full scent-swap process.

What are the signs that cat flu needs a vet?

Call your vet if: the cat stops eating for more than 24 hours, has coloured eye or nose discharge (yellow or green), develops laboured breathing, has mouth ulcers preventing eating, or shows sudden deterioration after seeming to improve. Our when to call the vet guide lists the urgency thresholds for each sign.

Cat Flu Outbreaks in UK Shelters 2026: What Owners Need to Know

What happened

Between July and October 2026, multiple UK cat rehoming centres — including Cats Protection branches in the East Midlands, Greater London, and South Wales — reported elevated rates of upper respiratory disease consistent with FCV and FHV-1. A subset of cases showed atypical signs including facial oedema and limb swelling, consistent with virulent systemic FCV (VS-FCV), which carries a higher mortality rate than typical FCV.

The Animal and Plant Health Agency (APHA) began preliminary molecular typing of submitted samples in September. Initial sequencing suggests at least one circulating strain has partial divergence from the strains represented in current commercially available vaccines — though the clinical significance of this is still being assessed.

Key facts

Cat flu is caused by feline herpesvirus (FHV-1) and/or feline calicivirus (FCV) — not related to human influenza
Both viruses are included in the core cat vaccination schedule
VS-FCV (virulent systemic calicivirus) is a severe variant that can affect vaccinated cats
Shelter environments are high-transmission settings due to density, stress, and mixing of cats with unknown histories

Who is most at risk

The cats most vulnerable to severe disease are:

Unvaccinated cats or those with lapsed boosters — maximum disease severity, no prior immunity
Kittens under 16 weeks — primary course may not be complete; maternal antibodies declining
Immunocompromised cats — FIV-positive, on immunosuppressive medication, or with concurrent illness
Newly rehomed cats — stress of rehoming suppresses immune function and increases susceptibility to all pathogens
Previously infected FHV-1 carriers — stress reactivates latent herpesvirus, which can be transmitted to others

If you have recently adopted a cat

Book a vet appointment within 48–72 hours of bringing the cat home — even if it appears healthy. Shelter cats can be incubating infection without signs. Request vaccination history and ask whether the practice has seen any cat flu cases recently.

Keep the new cat isolated from any resident cats for a minimum of seven days, extending to 14 if any respiratory signs appear. Even mild sneezing warrants extending the isolation period. Follow the full introduction protocol in our guide to introducing a new cat to a resident cat.

Protecting resident cats

If your resident cat's vaccination booster is overdue, this is the moment to book it. Core vaccines covering FHV-1 and FCV are the primary protection against severe cat flu disease. Full schedule details are in our cat vaccinations guide.

There is no specific antiviral treatment for FHV-1 or FCV — management is supportive. Cats with suspected cat flu should be isolated from other cats, kept warm and hydrated, and seen by a vet if they stop eating or develop worsening signs. Our when to call the vet guide describes the threshold for urgent action.

FHV-1 carriers. Cats that recover from herpesvirus infection remain latent carriers for life. The virus can reactivate during stress — rehoming, a new pet, illness, or even a vet visit — and shed to other cats. This is one reason rescue cats should be kept isolated initially even after apparent recovery.

Cat flu outbreaks in UK shelters 2026: what owners need to know

What happened

Who is most at risk

If you have recently adopted a cat

Protecting resident cats

Frequently asked questions