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FIV Vaccine Isn't a Sure Shot

Denise Flaim | Animal House

August 20, 2002

In recent weeks, vets and cat owners alike have been abuzz over the newest vaccine to hit the market: Fel-O-Vax FIV, the first-ever vaccine for Feline Immunodeficiency Virus, or FIV.

But some are buzzing for different reasons.

On the one hand, there's a clear need for an FIV vaccine: According to the American Association of Feline Practitioners, up to one in 12 cats tests positive for the virus. Like HIV in humans, FIV can severely weaken the immune system and pave the way for secondary infections. But despite being nicknamed "the feline AIDS," FIV cannot be transmitted from cats to humans.

Arne Zislin, a veterinarian at Kansas- based Fort Dodge Animal Health, which manufactures the vaccine, says Fel-O-Vax FIV has been out for five weeks, and things have been "very, very quiet" in terms of vets and owners reporting adverse vaccine effects.

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According to Fort Dodge, the vaccine has an 84 percent efficacy rate - that is, in a clinical trial, 84 percent of animals did not contract the disease when exposed to it. And the vaccine is unique in that it not only prevents the disease but forestalls infection as well, effectively stopping the virus from penetrating cells and integrating into a cat's DNA.

"I have no reservations about using this vaccine," says veterinarian Eileen Rowan of Bayville Animal Hospital, who started giving the vaccine series - three inoculations spaced two weeks apart - several weeks ago.

But veterinarian Jonathan May of Roslyn Greenvale Veterinary Group in Greenvale takes a different position, echoing the concerns of some feline practitioners who feel the vaccine was rushed onto the market too quickly.

First, the 84 percent efficacy rate is misleading, he says, because "it's not taking into account the natural immunity that some cats have to the disease without the vaccine." Other concerns: that the number of cats tested was not large enough and that other trials showed lower rates of immunity than the 84 percent figure the company is touting. (In response, Zislin of Fort Dodge says that the FIV vaccine was tested in the same way all the company's other feline vaccines were, and he says that the lower efficacy rate - 60 percent - was an earlier, prototype formulation of the vaccine, and not the current one on the market.)

But perhaps the biggest concern about the new FIV vaccine is that once a cat is vaccinated, tests for the disease will always show a false positive. Which means that if you decide to adopt a stray cat and he tests positive for FIV, you won't be able to tell if he actually has the disease, or is just vaccinated against it.

Since many shelters routinely euthanize FIV-positive cats, the mix-up could be the difference between life and death for some cats.

"The bottom line is, if this vaccine is wonderful and spectacular, why isn't it out there for people?" asks May rhetorically.

Because many vets and owners are concerned about vaccine-related sarcomas - cancerous tumors that can develop at the injection site - Fort Dodge is offering a $1,500 payment toward the treatment of any documented case caused by the vaccine. (The payment for services is made directly to the veterinarian, not the owner.) If the animal died before receiving treatment, Fort Dodge has said it will donate an equivalent amount to the American Veterinary Medical Association's Vaccine Associated Feline Sarcoma Task Force. This $1,500 payment is applicable to any of its feline vaccines, not just the one for FIV.

When it comes to that new vaccine, most vets are in agreement about one thing: A cat's individual lifestyle has a huge bearing on the likelihood he or she will exposed to the disease. Since FIV is transmitted via saliva and blood - particularly through bites - indoor cats who do not live with FIV-positive cats have a limited chance of contracting the disease. Most at risk are fight-picking male cats who run loose, especially in areas where FIV is clustered, often thanks to a large feral-cat population.

But even in those cases, May thinks the vaccine poses enough problems that it should be used "sparingly - if at all."