Re: Vaccine-Induced Tumors In Cats

Even though this pertains to vaccination of cats, it's worthwhile to do a validating risk versus benefit analysis. It's very important to apply this kind of probability analysis to the real (or perceive) risks of any vaccination with any species.

The University of Google provides numerous references reporting the incidence of vaccination induced sarcoma in felines variously from 1 to 4 cases per 10,000 feline leukemia virus (FeLV) vaccinations. How does this bounce against the risk of the average domestic cat coming in contact with another cat infected with FeLV?

A study done in two large U.S. cities:

http://www.ncbi.nlm.nih.gov/pubmed/12418520


From the study’s abstract:

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OBJECTIVE:
To determine prevalence of FeLV infection and serum antibodies against feline immunodeficiency virus (FIV) in unowned free-roaming cats.

DESIGN:
Cross-sectional serologic survey.

ANIMALS:
733 unowned free-roaming cats in Raleigh, NC, and 1,143 unowned free-roaming cats in Gainesville, Fla.

RESULTS:
In Raleigh, overall prevalence of FeLV infection was 5.3%, and overall seroprevalence for FIV was 2.3%. In Gainesville, overall prevalence of FeLV infection was 3.7%, and overall seroprevalence for FIV was 4.3%. Overall, FeLV prevalence was 4.3%, and seroprevalence for FIV was 3.5%. Prevalence of FeLV infection was not significantly different between males (4.9%) and females (3.8%), although seroprevalence for FIV was significantly higher in male cats (6.3%) than in female cats (1.5%).

CONCLUSIONS AND CLINICAL RELEVANCE:
Prevalence of FeLV infection and seroprevalence for FIV in unowned free-roaming cats in Raleigh and Gainesville are similar to prevalence rates reported for owned cats in the United States. Male cats are at increased risk for exposure to FIV, compared with female cats.
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So… If you have a cat that is exclusively an indoor dweller, the FeLV risk is extremely low. But about 4% to 5% (that’s roughly 1 of 20) of the non-house dwelling cats potentially encountered by your cat outdoors in a typical U.S. city will be infected with FeLV. Can you really control the contacts of your cats if not sequestered at all times indoors?

Here's your "do the math" potential risks question: 1 to 4 per 10,000 risk versus 1 per 20 risk?