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Vaccinations and Feline Cancer

The switch in 1985 from a rabies vaccine that contained a live rabies virus (modified to make it harmless) to one that used a killed virus (with ingredients added to “up” the immune response it provoked) coincided with a puzzling rise in feline sarcoma, a deadly type of cancer that is difficult to treat. Veterinarians noticed that these sarcomas were turning up near vaccination sites and in 1996, the American Veterinary Medical Association, American Animal Hospital Association, American Association of Feline Practitioners and Veterinary Cancer Society jointly formed the Vaccine-Associated Feline Sarcoma Task Force (VAFSTF) to investigate the problem.

Complete answers remain scarce, but the evidence that’s emerged so far suggests that while the benefits of rabies vaccination still outweigh its risks, veterinarians can reduce the potential for feline sarcoma with certain practices. The VAFSTF recommends that rabies vaccines be given in the right rear limb to reduce the risk of feline sarcoma to cats—making the injection site easier to monitor and care for. The group is looking into other ways to cut the risk even further. Meanwhile, the Rabies Challenge Fund (RCF) was founded in 2005 to determine the duration of immunity conveyed by rabies vaccines in hopes of convincing lawmakers that annual rabies vaccines are excessive.

Currently, rabies booster vaccines are labeled and administered based on local laws, not according to scientific data on the duration of their effectiveness, says Roberta Lillich, DVM, president of the American Association of Feline Practitioners. In fact, one vaccine manufacturer produces multiple versions of the identical vaccine with different labels according to the locally mandated vaccination schedules. Many localities still require yearly rabies boosters, even though existing vaccines have been shown to last years beyond their expiration dates.

“There is solid evidence that a single rabies vaccine produces multi-year immunity,” says Julie Levy, DVM, PhD, at the University of Florida in Gainesville. But finding out exactly how long vaccines can protect against rabies requires expensive, complicated studies and neither vaccine makers nor local governments have much incentive to fund these studies. The RCF aims to fill this gap by funding trials they hope will eventually extend the required interval for rabies boosters to five and then to seven years.