Without treatment, cats with FIP typically live days to weeks after symptoms appear. The effusive (wet) form progresses fastest, with median survival times as short as 8 days in clinical studies. The non-effusive (dry) form moves more slowly, with survival measured in weeks to months. But antiviral treatment has fundamentally changed this picture: roughly 85% of treated cats now achieve remission and go on to live normal lives.
Survival Without Treatment
FIP was considered universally fatal until very recently. In two controlled clinical trials, cats receiving only supportive care (steroids and symptom management) survived a median of just 7.5 to 8 days. That number reflects the effusive form, which accounts for about 75% of cases and progresses rapidly as widespread inflammation causes fluid to build up in the abdomen or chest.
The non-effusive (dry) form moves at a different pace. Because the cat’s immune system partially contains the virus, limiting it to a smaller number of cells in specific organs, cats with this form can survive weeks to months. Some rare cases have lingered even longer, though the disease still progresses. It’s also worth knowing that cats can shift between forms: a dry case can develop fluid accumulation and become wet, or vice versa.
How Antiviral Treatment Changed the Outlook
The antiviral compound GS-441524 has turned FIP from a death sentence into a treatable disease. A systematic review covering 650 cats treated with GS-441524 found a combined success rate of 84.6%. Of those cats, 80.6% achieved remission with their first treatment course, and another 4% reached remission after relapsing and completing a second round.
Success rates vary by the type of FIP:
- Non-effusive (dry) FIP: approximately 88% success rate
- Mixed FIP (both wet and dry features): approximately 85%
- Effusive (wet) FIP: approximately 78%
Cats that respond to treatment and complete the full course can go on to live normal, healthy lives with no ongoing disease. “Remission” in these studies effectively means cure: the virus is cleared, and the cat returns to full health.
What Treatment Looks Like
The standard treatment course is 12 weeks of daily antiviral medication, followed by a 12-week observation period. Some cats, particularly younger ones with the wet form, can be cured in as little as 8 weeks. Cats with neurological or eye involvement require higher doses for the same 12-week duration.
During the observation period after treatment ends, your vet will monitor bloodwork and watch for any return of symptoms. There’s no single blood test that reliably confirms a cure, so this waiting period is an important part of the process. Most cats show dramatic improvement within the first week or two of treatment, with appetite returning, energy levels rising, and abdominal fluid resolving.
Cats With Neurological or Eye Involvement
When FIP affects the brain or eyes, the outlook is less favorable but still far better than it once was. About 26% of cats in the large systematic review had neurological signs (seizures, uncoordinated movement, behavior changes) or eye inflammation. Their combined success rate was around 74.5%, compared to 84% in the overall population. These cats need higher antiviral doses because the drug must cross into the brain and eye tissue, but three out of four still achieve remission.
How Often Cats Relapse
Relapse is the main concern after treatment. In a study of 307 treated cats, about 11% relapsed. Nearly half of those relapses happened during the initial treatment course itself, at a median of 40 days in. The other half occurred after treatment ended, typically within the first two months: 83% of post-treatment relapses happened within 60 days of stopping medication.
Late relapses are uncommon but possible. A small number of cats in that study relapsed at 90, 390, and even 450 days after treatment. This is why continued monitoring matters even after a cat appears fully recovered. The good news is that many relapsing cats can be successfully retreated with a second course or switched to a different antiviral.
Signs That FIP Is Progressing
If you’re watching a cat with suspected or confirmed FIP, the progression depends on the form. Wet FIP tends to announce itself with a visibly swollen abdomen or labored breathing as fluid fills the belly or chest. Cats lose weight despite a normal or even increased belly size, develop fevers that don’t respond to antibiotics, and become increasingly lethargic.
Dry FIP develops more gradually. You may notice weight loss, persistent low-grade fever, and a general decline in energy over weeks. If the disease involves the nervous system, you might see wobbliness, difficulty walking, head tilting, or seizures. Eye involvement can cause visible cloudiness, color changes in the iris, or unequal pupil sizes. Once clinical signs are apparent and progressing, the disease accelerates without antiviral intervention.
Factors That Affect Survival
The single biggest factor is whether the cat receives antiviral treatment. Beyond that, the form of FIP matters: dry FIP responds best, wet FIP is slightly harder to treat, and neurological involvement lowers the odds. Combination therapy (using GS-441524 alongside another antiviral) produced success rates near 95% in pooled data, compared to 83% for the antiviral alone, though combination protocols are newer and less widely studied.
Age plays a role in a different way. FIP disproportionately strikes young cats, typically under two years old. These younger cats often respond quickly to treatment. The speed of diagnosis also matters: cats treated earlier in the disease course, before severe organ damage or deep neurological involvement, tend to have better outcomes. If your cat has been diagnosed, starting treatment quickly gives the best chance of a full recovery and a normal lifespan.