After all, vaccines are a standard in health care. We vaccinate our children against hepatitis, polio and influenza when they're infants and toddlers, giving up to two boosters of some vaccines until puberty. But then we stop.

Not with our pets, though. In fact, we continue bolstering the immunity of our pets until they are well into their senior years. That has spawned a debate as fierce as any fighting pit bull: To vaccinate or not to vaccinate.

Many veterinarians believe the practice of annual vaccinations is an unnecessary evil, responsible for such diseases as allergy, seizures, anemia, even cancer. They say vaccinations make our animals vulnerable to some of the top diseases plaguing our pets, and that rather than building up immunity we are overwhelming their immune systems. Others would rather stick to tradition and say that vaccinating has warded off the most deadly animal diseases over the past 30 years, so why question it now.

Lack of Scientific Evidence

Dr. W. Jean Dodds, president of the nonprofit animal version of the Red Cross called Hemopet, was one of the pioneers of the vaccine debate, an issue she says has been percolating for the past 10 years. She says as the profession started looking into exactly how the recommendations for annual vaccines arose, they started realizing that they were just that — recommendations. And in fact, they were not based on scientific evidence.

Dodds says that after 20 years of following the United States Department of Agriculture and the drug manufacturer's recommendations to make annual vaccines a standard in veterinary care, professionals who first challenged the standard school of thought were considered rebels. Her arguments were challenged by other veterinary professionals whose belief in the duty to vaccinate was galvanized by episodes such as the deadly parvo virus epidemic in the late 1970s that killed thousands of dogs and was only halted by mass administration of the parvo vaccine.

But Dodds says an unfortunate observation led many vets to begin to reconsider current vaccination protocol. In 1991, three years after Pennsylvania issued a mandatory rabies vaccination requirement for cats, Dr. Mattie Hendrick's lab at the University of Pennsylvania noted a connection between the surprising increase in the number of sarcomas, or cancerous tumors, and vaccination in cats. It seemed that in some cats, rabies vaccinations were leading to an inflammatory reaction under the skin.

Shortly after, researchers at the University of California at Davis showed that feline leukemia vaccines were also likely to cause sarcomas, and to an even greater degree than the rabies vaccine. Further investigating led researchers to estimate the prevalence of vaccine-induced sarcomas to be as much as one cat in 1,000, or up to 22,000 new cases of sarcoma a year.

Soon, veterinary professionals began to suspect vaccination as a risk factor in other serious auto-immune diseases. Researchers surmised that, in some animals, vaccines were stimulating the animal's immune system against his or her own tissues, leading to potentially fatal diseases such as auto-immune hemolytic anemia (AIHA) in dogs. Researchers began to suspect delayed vaccine reaction for the cause of such chronic conditions as thyroid disease, allergy, arthritis and seizures in cats and dogs.

Such observations led to a 1995 Journal of the American Veterinary Medical Association article that concluded there is "little scientific documentation that backs up label claims for annual administration of most vaccines," and that the only vaccine tested routinely for duration is the rabies vaccine. In addition, the article suggested that though some vaccines should be given annually, giving others only every few years would be sufficient because of potential risks associated with them.

Hesitation to Vaccinate

Dodds says that in her own practice, she only vaccinates when necessary. Rather than automatically giving boosters, Dodds gives annual titers, or tests, to check the level of antibodies (disease fighting cells) in the blood to determine if boostering is necessary. Though she expects that immunity would be conferred for life, she says that titers offer "an added measure of security."

Though many vets have in fact begun to change their vaccination habits, many continue to administer annual shots. Dodds believes that the resistance is not so much a financial issue since vets should still asks clients to come in for an annual check-up and titers. Rather, it's more about changing attitudes.

"For decades we were told that this is what we had to do," Dodds says. "The USDA put the recommendation on the label. Our confidence was totally shaken up."

Non-Vaccination a Greater Danger?

Still, many vets believe it's too early to change procedure. The say that until more is known about the immunity conferred by some vaccines, it's best to take a conservative approach. They emphasize the fact that annual vaccinations have been effective at decimating the incidence of formerly common, potentially lethal viral diseases such as feline panleukopenia, rhinotracheitis, feline leukemia, canine distemper, hepatitis and canine parvo virus. And with the incidence of the deadly feline leukemia virus so high, it is too hard and too risky to determine which cats are at risk.

Dr. Donald Klingborg, former Chairman of the Council of Biologic and Therapeutic Agents of the American Veterinary Medical Association (AVMA) and Assistant Professor at the University of California at Davis, says that while the vaccination issue is a complicated one, nonvaccination is a major error.

"In most cases, the threat to the animals' health from nonvaccination is much greater than vaccination," he says. "The diseases are real, severe and common."

Klingborg says the vaccination debate could be settled by more information on the duration of immunity most vaccines impart.

Conclusive Answers Difficult

But while vaccine companies are under no legal obligation to demonstrate duration of immunity, that question may remain unanswered for some time.

Dr. Susan Wynn, a Georgia-based veterinarian and former board member of the American Holistic Veterinary Medical Association says that the problem with obtaining immunity duration information is monetary and political.

"This information would have to be gained by challenge studies in which you give viruses to animals inoculated over five to 10 years ago," she says. "You would have to keep those animals in a controlled environment for this time — only drug companies have that kind of money."

Wynn says that for the drug companies, the decision is based on priorities — it's either more products or immunity studies, not both.