Best Immunity

Feline vaccines are creating better immunity as research uncovers new methods and challenges.

Stephanie Staton

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Vaccines have come a long way since the first one was developed to prevent smallpox in the 1700s. Ongoing research has resulted in continuing advancements for humans and animals alike.

Many of the most recent advancements have been in the realm of feline vaccines, enough that the American Association of Feline Practitioners (AAFP) plans to appoint a committee to establish its second set of guidelines for vaccinating cats.

Elizabeth Colleran, DVM, president of the AAFP and owner of Chico Animal Hospital in Chico, Calif., says her organization last published recommendations for feline vaccines in 2006.

“We’re due for an update and a review of all of the protocols that were recommended then,” Dr. Colleran says. “That work hasn’t been done yet.”

Establishing best practices is a work in progress even five years later.

“Up until then, there weren’t any science-based guidelines,” she says. “We’re still feeling our way.”

While many veterinarians rely on the recommendations of the American Animal Hospital Association (AAHA) for canine vaccines, no other major veterinary organization has issued guidelines for cats, Colleran says. She expects AAHA and other organizations to play major roles in the new AAFP guidelines. Colleran notes that her group and AAHA recently collaborated on some work regarding pain management and says similar teamwork will help establish the best possible vaccine guidelines.

“What we’re working on now is collaborating with the groups that care about this and putting our heads together,” Colleran says.

Jason Merrihew, AAHA’s associate public relations manager, echoes Colleran’s enthusiasm for collaboration.

“Although I can’t comment on potential projects, AAHA has collaborated with AAFP on guidelines and other projects that have been valuable to the veterinary profession, cats and cat owners,” Merrihew says. “AAHA will be meeting with AAFP … to discuss future collaborative projects.”

The panel that produced the AAFP’s 2006 recommendations included researchers such as the late James R. Richards, DVM, of Cornell University and Michael Lappin, DVM, Ph.D., Dipl. ACVIM, of Colorado State University, whom Colleran said recently produced some very significant research on feline vaccines.

Injection-Site Sarcomas

Though rare, vaccine-associated sarcomas are a concern to many veterinarians working with cats.
Alice Wolf, Dipl. ACVIM, ABVP (Feline), says research and experience points to these tumors being caused by vaccine adjuvants.

“It’s not politically correct to call them vaccine-associated sarcomas; we’re supposed to call them injection-site sarcomas,” she says. “But the thing is, before the mid-1980s, we didn’t see them and we used to give tons of things by injection. If it was just a function of traumatizing the skin, we should have seen this problem before the mid-1980s.”

Once adjuvants were introduced, veterinarians began seeing more of these sarcomas at injection sites, she says. They appeared to be connected with the tumors by virtue of doing their job, Wolf says.

“It causes chronic inflammation at the vaccine site,” she says. “And that’s what it’s designed to do. The adjuvant creates inflammation, which recruits immune cells to respond and create immunity.”

Elizabeth Colleran, DVM, president of the American Association of Feline Practitioners, says vaccine-associated sarcomas are linked to a number of factors, including adjuvanted vaccines.

“I think the evidence is pretty compelling that the adjuvanted vaccines could be implicated in that cadre of cats that get sarcomas,” she says. “But we also know that there’s a genetic predisposition for them. There’s localized inflammation that occurs in all vaccines. That inflammation has been sort of morphed into neoplastic cells or cancer cells. There may be some way in which the accelerator actually creates more of a localized inflammatory response and may be implicated in this constellation of things that cause the sarcoma.”

Many veterinarians are no longer using adjuvanted vaccines, Colleran says, but some practices and shelters continue to use them because they are less expensive than non-adjuvanted vaccines.

“Most of the shelters now are really trying to have cats adopted that are vaccinated, wormed and neutrered, so they’re ready to go to good homes,” she says. “That’s a pretty big burden for a shelter to take on. If there’s a more affordable option, they are likely to take it.”

Wolf says the practitioner should present the best and safest option for patients.

“Oftentimes they use adjuvanted vaccines due to costs, but you have to put things in perspective,” she says. “Let’s say the difference is $5. That’s a couple gallons of gasoline. What is better safety worth?”

Both Colleran and Wolf agree that vaccine-associated sarcomas are rare, though the numbers vary depending on the research involved, Wolf says.

“I’ve read 1.3 per 1,000 cats and 1 in 10,000,” she says. “The one in 10,000 may not sound like very much, but if that’s my cat, that’s too much.”

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“We get the best of the best,” she says. “We empanel a group of experts and turn them loose on the issue, and they do an enormous amount of research.”

Alice Wolf, DVM, Dipl. ACVIM, ABVP (Feline), an emeritus professor in small animal clinical sciences at Texas A&M University, has been prolific in research and publications on feline vaccines.

She says vaccines are getting further from the original model of injecting live virus and benefiting from genetic research.

“It’s no longer about killed vaccine and it’s rarely about modified live,” she says. “When you look at humans, it’s all about vectored vaccines. The object is to reduce adverse events. You can focus the immune response and use less antigen.”

Vectored vaccines for cats utilize virus cells not known to infect cats, Wolf says—often canary pox—to carry what is needed to protect the cat from rabies or another disease.

“It acts like a modified live, but it only contains very small pieces of the DNA of the virus,” Wolf says. “They snip out the pieces. The canary pox virus acts like a little submarine; it transports the DNA. And because it’s not the whole virus, there’s no chance of infection.”

How to Deliver

Vaccine formulas on the market now and under development are changing, Wolf says, and she believes the veterinary field will see more variation in delivery methods, including alternatives to the hypodermic needle. Intranasal vaccines on the market may be more difficult to administer, Wolf says, but they provide more immunity at the site where respiratory infections take place.

“You’re getting the best protection where the organisms would actually invade,” she says.
Also likely to increase in popularity is the transdermal vaccine, currently in use for cats only with Merial’s feline leukemia vaccine, she says. In addition to her work at Texas A&M, Wolf consults for Merial. Transdermal vaccines are being used with humans as well.

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“The advantage to the transdermal delivery is that there are specific cells in the layer right below the skin that are called dendritic cells,” Wolf says. “They recognize the components of the vaccine and alert the cells of the immune system to come and respond. You get more of a response from a small amount of the vaccine. It’s better for stimulating cell-mediated immunity, which is the most important for feline leukemia and FIV.”

How Often?

Vaccine frequency is likely to change in the coming years, Colleran says. “There have been a lot of studies that show longer duration of immunity,” she says.

Wolf agrees.

“I think that one of the main issues for me is still getting more people on board with extended vaccination protocols,” she says. “Many vaccines are effective for three years, although they’re not labeled that way because they were not approved that way by the FDA.”

Some vaccines may protect cats even longer.

“It’s been shown for feline parvo virus that excellent protection in kittens will probably protect them for life,” Wolf says. “There are also some vaccines for which we can’t create 100 percent protection because of the nature of the antigen.

“We see still a few animals that have been vaccinated that may show mild clinical signs when they’re exposed to the agent. The vaccines don’t provide a solid protection, however vaccinating more often doesn’t improve that.”

Veterinarians in practice are deciding on schedules for their feline patients based on a number of factors, including lifestyle, often with the less-is-more approach Wolf and Colleran describe.

“We pretty much just do every three years for most of the vaccines and we only do feline leukemia if they’re going outdoors,” says Abigail Bertalan, DVM, an AAFP member in practice at Red Bank Veterinary Hospital in Red Bank, N.J. “We’ve decreased the frequency of vaccines. We have a lot of cancer patients we don’t even vaccinate. We’ll give them a waiver for rabies.”

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U.S. researchers continue to work to find the best ways to produce immunity in cats with fewer adverse events and on the best possible schedule. The growing body of literature on the subject will guide the AAFP and veterinarians in making the best choices for feline patients going forward.

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