The first reports of vaccine site-associated sarcomas were published in the early 1990s. These lesions have caused widespread concern in the veterinary community since then, and the causal relationship between sarcomas and vaccines for rabies and FeLV is generally accepted. This study was designed to quantify incidence of vaccination practices, postvaccination reaction, and vaccine site-associated sarcomas in cats in the United States and Canada. Practitioners were directed to a Web page by a variety of announcements in journals, magazines, Web sites and by speakers at selected meetings. Applicants were confirmed to be licensed veterinarians and given forms to submit data. Data were collected from January 1, 1998, to December 31, 1999. Follow-up e-mails were sent to all participants requesting information on additional sarcomas diagnosed from the time of vaccination until December 31, 2000. During the 2-year study period, 21 sarcoma cases were reported and 14 additional sarcomas were reported during the 1-year follow-up. Of these, only 2 reports fulfilled the diagnostic criteria to establish incidence specifically for vaccine site-associated sarcomas.

The authors cited several criticisms of the study: veterinarians who withdrew from the study after enrolling, which led to a smaller sample size than was initially hoped for, and that the number of reported sarcomas could be lower because owners did not bring the cat back to the veterinarian who vaccinated it. Although not a true statistic, the incidence cited in the study was 0.63 sarcomas/10,000 cats vaccinated per year, suggesting that the disease can still be considered rare. Regardless, a significant number of vaccinated cats do develop the disease.

The findings of postvaccination reactions are reassuring-98% resolve without medical intervention, 96% of these within 3 months and 100% within 4 months.

World Wide Web-based survey of vaccination practices, postvaccinal reactions and vaccine site-associated sarcomas in cats. Gobar GM, Kass PH. JAVMA 220:1477-1482, 2002.