DVM Magazine InFocus
july 2003

Analyzing the risk and benefits for vaccinations

Base vaccination recommendations on good science

By Hugh B. Lewis, BVMS, MRCVS, Dipl. ACVP
CONTRIBUTING AUTHOR

There is a great deal of literature including many books on the science behind risk/benefit analysis. I reviewed some of them prior to writing this article, but try as I might, I could not incorporate much into the task at hand, namely doing a risk/benefit analysis of vaccination in pets. One thing I did learn was that one can't just do a risk/benefit analysis: there must be a purpose in mind, e.g. what is the most effective approach to the control and prevention of disease X, or, what is the safest approach to the prevention of disease X? From the perspective of the pet owner, the purpose behind vaccination could be: what vaccines are necessary for my pet, and are these vaccines safe for my pet? I will focus on these last two questions since the decision belongs with the client, but the veterinarian, being the expert, is expected to advise the client as to what is best for the pet

The process leading to a vaccination decision for an individual pet involves the owner/owning family and the veterinarian. The patient is the pet, and both the veterinarian and the owner presumably want to do what is best (safe and effective protection) for the pet The veterinarian is expected to be an advocate for the pet and not to have another agenda The attitude of the owner probably reflects the strength of the bond between owner and pet and the place of the pet within the family structure. It also would be expected to reflect the personal risk acceptance profile of the owner, his or her knowledge and understanding of vaccination, as well as the trust and confidence he or she has in the veterinarian.

A number of groups, including the American Veterinary Medical Association (AVMA), American Animal Hospital Association (AAHA) and the vaccine manufacturers, advocate that a risk/benefit analysis be done on each pet to be vaccinated rather than instituting species-specific vaccine protocols for all pets seen by the practice. This article examines that notion and explores what such an approach would entail.

Factors in the veterinarian's decision-influencing role would probably include:

• Fundamental knowledge and understanding of the science of vacci-nology;
• Practice philosophy/goals, e.g. evidence-based and high quality medicine;
• Standards adhered to: internally generated or externally driven, e.g. AAHA;
• Level of devotion to and understanding of the scientific process;
• Level of understanding of Aescu-lapian authority in pet practice, or the importance of being an advocate for the pet;
• Knowledge of the diseases and disease organisms in question and their local prevalences, mechanisms of spread, ease of diagnosis and treatments.
•Knowledge of the likely level of exposure by the particular pet to diseases;
• Status of the pet's immune system;
• The efficacy of the vaccine as well as the incidence of adverse effects;
• Respect for the opinions and sensitivities of the client

Factors in the owner's decision-making process:

•Trust in the advice received from the veterinary team, particularly the doctor;
• Level of risk the owner will tolerate;
• Financial priorities of the owner;
•Strength of the bond between owner pet Is the pet a family member?
Each of these factors can influence vaccination decisions.

Knowledge, understanding
Veterinarians know that vaccination is the most cost-effective strategy for controlling infectious diseases in pet populations, and most would agree that it is far better to prevent disease than to let it occur and then treat it Vaccination is a medical procedure that does not always induce immunity and can cause side effects, which in rare cases, may be severe. Veterinarians also appreciate that vaccination is a population-based disease control strategy and understand that disease in individual pets is a reflection of the level of disease threat, the level of immunity in the individual and in the local pet population as well as the presence or absence of other modifying factors. It is important that clients also understand the limitations of vaccination.

Practice goals, standards
This will vary from practice to practice. Practices may establish their own standards or may follow the lead of organizations such as veterinary schools, AAHA, and veterinary medical associations. At Banfield, we set our own standards. These reflect our commitment to provide pets with the same care we want for ourselves. We are a bond-centered, evidence-based practice, and we are committed to making life better for families. We believe that pets should not be a threat to other family members. We are committed, therefore, to preventing diseases that pose a threat to people and to preventing diseases that pose a significant threat to pets. As such, we recommend vaccination of pets against:
•All diseases of pets that are endemic to the United States and are associated with significant morbidity and mortality - especially those for which there are no readily available diagnostic tests or effective therapy (e.g. distemper, parvovirus, pan-leukopenia, FeLV, FTV, rabies);
• Chronic diseases or diseases with chronic sequelae that affect a pet's quality of life (e.g., Lyme disease, feline respiratory disease).
• Diseases that are directly or indirectly transmissible from pets to the human
members of the family (e.g. leptospirosis, giardiasis, rabies). Practices that have a different philosophy will presumably recommend a different mix of vaccines, and practices with a single location may well tailor their recommendations to only those diseases they encounter locally.

Regarding revaccination intervals, we, like many practices, take the position that this should be dictated by scientific evidence that has been proven to be safe and effective in field studies. In cases where such evidence is lacking or deemed insufficient, we will recommend vaccination protocols that have proven over time to provide excellent protection and minimal adverse events. Other practices may choose to align with the recommendations of their local referral practice, school of veterinary medicine or AAHA, while trusting that such groups know what they are doing.

As professionals, veterinarians should be prepared to stand behind their recommendations. For example, our practice warrants the efficacy and safety of the vaccines we use. If they fail and a pet develops the disease it was vaccinated against, the costs involved in the treatment will be
borne by the practice. If adverse events follow vaccination, the practice will bear the costs involved in treatment We, therefore, have a very significant stake in using safe and effective vaccines.

Good science
Much confusing information concerning vaccination is being published in the veterinary press and significant changes in vaccination strategy are being proposed and debated. Some of the changes advocated are based on preliminary experimental data that has not been confirmed or tested in the field. The scientific process as applied to medical therapies is well established Experimental studies giving rise to new evidence should be repeated and confirmed, tested in the field for clinical efficacy and safety and then subjected to peer review. New strategies should not be based on preliminary data and anecdotal reports. Arguments based on opinions that field studies will never be done because they are too expensive should be dismissed out of hand. As a profession, we need collectively to do what is necessary to confirm significant new findings and support warranting changes in disease prevention strategies. This is our practice's position. Others believe there is sufficient convincing evidence to warrant major changes in vaccination strategy.

Aesculapian authority
For many owners, pets are now members of the family. People want their pets to be happy, healthy and long-lived, and their healthcare is viewed as very important. The role of the veterinarian is changing; increasingly; we are expected to be advocates for doing what is best for the pet just as pediatricians are expected to be advocates for doing what is best for the child. People expect this of pet practitioners. In other words, they are willing to trust that the advice from their veterinarian is what is best for their pet This is very different from the traditional role of veterinarians in providing a set of options for the animal owner that range in cost, quality and sophistication.

Disease prevalence
Implicit in the commitment to the prevention of disease is an understanding that the disease is a real threat to the pet and/or the family. Unfortunately, an up-to-date and reliable source of disease prevalence data by region and by pet species is rarely available. As a national practice with hospitals across the country, we are naturally concerned with diseases that are endemic to the United States. In a stand-alone practice, the concern may well be more localized In our experience, the diseases we deal with do occur across the country: We see heart-worm in the Northwest and even in Las Vegas. Lyme disease is found in many states, not just the Northeast and Great Lakes region. The mobility of our society, the fact that many people travel with their pets (truck drivers, RV owners, vacationers) and the fact that diseases and vectors have no respect for state boundaries all contribute to their inexorable spread throughout the country. This raises an important medical question: When is it appropriate (or ethical) to prevent disease? Do we wait for a disease to become endemic in an area before it is OK to prevent it? Or, do we prevent it from becoming endemic? I think the public's response to SARs and monkeypox scares suggest the sensible answer.

The level of likely exposure of any particular pet to a disease-producing organism is usually unknown unless the pet is kept isolated from other animals and people. A few years ago, we surveyed several hundred clients who claimed that their pets were kept indoors, therefore having little chance of exposure to potential pathogens. Surprisingly, almost 40 percent of them readily admitted upon follow-up questioning that their pets "escaped once in a while," only "went outside when supervised" and "loved walking around PetsMart," or did not get on with their other "mainly outside"
pet. The definition and significance of indoor pet may thus be suspect. Also, I do not believe we can claim that a pet that visits a veterinary hospital is not at risk of exposure to disease. We should assume that they are at risk since most pathogens are quite hardy and can survive for variable periods of time in a hospital environment.

In view of the uncertainty associated with past exposure and the feet that neither veterinarian nor owner can confidently predict future exposure of the pet to disease threats, it makes sense to ignore this factor if there is any doubt at all and advocate vaccination.

Immune status
We do not know the immune status of most of the pets presented for vaccination, but unless they are very young, very old or known to be sick, we can reasonably assume that the pet will respond normally to vaccination. Immunity to specific diseases may be possible to assay (for some diseases at least), by monitoring neutralizing antibody levels. However, according to some authorities, measuring antibody levels in pets may not give reliable results. Thus, this is an area that remains largely unknown to us although it is a critical factor in the generation of an effective immune response in a pet.

Vaccine efficacy, adverse effects
To be licensed, a vaccine must be efficacious and safe and any label claims related to duration of protection must be backed up by challenge data. This does not necessarily mean that a new vaccine is efficacious and safe under all field conditions. Vaccination is a potent medical procedure and is associated with benefits and risks for the individual pet. Adverse effects, including some that are potentially serious, can be unintended consequences of vaccination. These are rare, invariably unpredictable and usually reflect an idiosyncratic reaction in a particular pet rather than being an inherent quality in the vaccine. The incidence of reported adverse effects to vaccines in our practice is .12 percent (12 per 10,000). This is based on an internal adverse effect reporting system and a database of several million pets. A higher percentage of these changes occur in smaller breeds than in the larger breeds. Most of them (>90 percent) are reflective of a positive immune response (the vaccine was effective) and include transient signs such as lethargy, inappetance, mild fever and pain and swelling at the injection site. Only one to two out of 10,000 pets seen at Banfield experience a potentially serious adverse event such as anaphylactic shock and collapse. Such effects invariably occur shortly after vaccination and, for the most part, are readily treatable. Cats can develop aggressive sarcomas at the site of vaccination. This is also rare, in our hands occurring to about one in 10,000 cats vaccinated. More research is needed to fully understand this phe-
nomenon, its pathogenesis and possible link to vaccines.

Overall, we do not think the incidence of adverse effects warrants not vaccinating a pet However, the risks of these potential adverse effects do need to be clearly explained to pet owners.

Client sensitivities
As stated above, we strongly advocate and explain what we believe is best for the pet, and this is done on a pet-by-pet basis, and is between the veterinarian and client. Clients select a practice or stay with a practice that shares a similar philosophy and attitude to pets and their care. The factors that impact the client's decision relate to the importance of the pet to their family (strength of the bond, family member or not), the confidence they have in their veterinarian and his/her advice, the level of risk that is tolerated by the client, and occasionally, the financial status of the family. Almost all clients want to do what is best for their pets, but occasionally, it cannot be done. In our experience, it is the strength of the bond between pet and family that is the major determinant As veterinarians, we must respect that.

The risk/benefit discussion
This basically comes down to the attending veterinarian advocating what he or she believes is best for the pet based on their practice's philosophy and the owner accepting or rejecting the advice based on the above sensitivities. The veterinarian's advice strongly influences the pet owner's decision. It is important, therefore, for a practice to develop a consensus opinion about health strategies such as vaccination. It is confusing for clients when professionals within a practice disagree among themselves. Indeed, it is confusing when professionals in different practices disagree among themselves.

Banfield advocates broad vaccine protection for pets. We recognize that the attending veterinarian is the only one who can make the final recommendation that takes into account the considerations previously noted.

The decision
Scenario 1: "Thank you, doctor, for advising us on the importance of keeping Buffy up to date on his vaccinations. I also appreciate being informed of the potential risks associated with vaccination. Buffy is an important member of our family and we want to do what is best for him. Please go ahead and vaccinate him."
Scenario 2: "I appreciate your view, doctor, but we have decided not to continue vaccinating Fluffy. My son found a lot of information about pet vaccination on the Web and we were shocked to learn that vaccines can cause cancer and other serious side effects as well as auto-destructive diseases in pets. They can even cause autism in children! I'm surprised that you don't know about all this. I'll leave the material for you to read. We also learned that most vaccines will protect a pet for years and annual shots are not necessary. Apparently, it is just a way for you veterinarians to make money!"

The vast majority of our clients consider their pets to be family members; they expect us to advocate what is best for their pet, and they generally accept our advice. It is so very important that as a profession we make decisions based upon good science. This means not making precipitous disease management changes before we have all the facts and are able to put new information into perspective. Important disease management decisions should be made on the basis of knowledge and field trial experience. DVM

Dr. Lewis is senior vice president of practice development for Banfield, The Pet Hospital. From 1986 to 1996, he served as dean of Purdue University School of Veterinary Medicine. Dr. Lewis also served in various positions for Smith Kline and French Labs for 10 years. He is a diplomate of the American College of Veterinary Pathologists and received his veterinary degree in 1965 from Glasgow University.
Dr. Lewis is a noted speaker and author. He has taught at the University of Pennsylvania School of Veterinary Medicine and Purdue.