Vaccination Facts vs. Fiction

By Richard B. Ford, DVM

The latest iterations of both the canine and feline vaccine guidelines have been available since the end of 2006. Clearly these guidelines have affected how veterinarians select and use vaccines, but questions and controversies remain.

The guidelines are available at www.aahanet.org and www.aafponline.org.

Why Vaccine Guidelines?

One of the most significant reasons for publishing vaccine guidelines is the fact that an unprecedented number of vaccines are available to veterinarians today. 

There are approximately 23 vaccine antigen types for the dog and 18 types for the cat.  Combined, there are over 180 proprietary (trade name) vaccines used in companion animal practices throughout the U.S.

But it’s not just the number of vaccines that drives the need for vaccine guidelines. 

With so many vaccines to choose from, veterinarians continue to express concern over the frequency of vaccination, the duration of immunity of the various vaccines in use, the important changes in vaccine technology (recombinant and DNA), vaccine safety, medical, legal, and ethical responsibilities associated with implementing a rational vaccination program, and much more.

Core Vaccines

Neither the American Animal Hospital Assn. Canine Vaccine Guidelines nor the American Assn. of Feline Practitioners Feline Vaccine Guidelines were written to define immunization standards for dogs and cats. Furthermore, they were never intended to represent a “universal vaccination protocol” applicable to all dogs and all cats in all practices.  

They are, simply, recommendations based on the most current, reputable science available today. Objectively, the vaccine guidelines provide reliable information with which veterinarians can develop a rational vaccination program that addresses realistic levels of risk for individual patients. 

There are two key points regarding implementation of core vaccines into a protocol for any practice.

First, it is the veterinarian’s prerogative as to which vaccines should be designated “core.” 

For example, although the AAHA Canine Vaccine Guidelines recommend distemper-parvovirus-adenovirus-2 and rabies as core vaccines, many veterinarians practicing in New England include Lyme disease vaccine as core.

Second, every veterinarian in the practice should agree on which vaccines are “core” for that practice. This is critical in communicating a clear, consistent vaccine message to clientele.

The recommendation that modified-live and recombinant core vaccines (distemper, adenovirus-2, and parvovirus for dogs; panleukopenia, herpesvirus-1 and calicivirus for cats) can be administered every three years without loss of protective immunity continues to be challenged despite publication of several supporting studies.

Although most, if not all, veterinary schools follow triennial vaccination recommendations, most practices do not. The fact remains, whether recommending triennial or annual boosters, both recommendations represent a reasonable and acceptable standard of care in veterinary medicine today.

Non-Core Vaccines

Vaccines designated “non-core” are considered optional. Any recommendation for administering a non-core vaccine should be based on reasonable assessment of the patient’s risk of exposure and infection. Furthermore, there are no three-year booster recommendations for non-core vaccines, only annual.  

Not surprisingly, much of the controversy surrounding vaccine selection and administration is centered on non-core vaccines.  

Feline leukemia vaccine, although listed as non-core, is highly recommended for all kittens through the first year of life. This is based on the premise that susceptibility for infection is highest among kittens and that kittens, despite an owner’s insistence that their cat will strictly be a “house cat,” tend to escape.

But that, too, is only a recommendation that many veterinarians tend not to follow. Adult cats that spend time outside unsupervised should receive an annual FeLV vaccination. 

The virulent systemic (VS) feline calicivirus vaccine has received considerable attention since its introduction in 2007. While the disease is, in fact, serious, the risk of exposure among household cats is extremely low. Despite marketing claims, there are no studies documenting increased prevalence in the U.S. 

Infections are considered to be rare and typically limited to shelter-housed cats. Furthermore, this vaccine has never been subjected to a heterologous challenge. The VS feline calicivirus vaccine should not be recommended for use in all pet cats. 

Determining the merits of intranasal Bordetella bronchiseptica vaccines versus the only parenteral vaccine has been challenging due to the lack of adequate challenge data. However, recent studies do give intranasal vaccines an edge. 

Dogs vaccinated with an intranasal vaccine and exposed to pathogenic B. bronchiseptica did not become clinically ill nor did they shed infectious bacteria.  

Parenteral vaccination, on the other hand, prevents development of clinical signs but does not appear to prevent shedding of virulent bacteria following exposure. 

The fact that all intranasal B. bronchiseptica vaccines also contain parainfluenza virus vaccine supports a role for use of the intranasal product.  Parainfluenza virus vaccine may be more immunogenic when given by the topical (intranasal) route. 

Whether to administer leptospirosis vaccine to an individual dog continues to be a challenging question. The obvious answer is, “It depends on the risk.”  

But risk for leptospirosis exposure and infection is difficult to define.  

Diagnostic testing is infrequently performed in practice and results can be difficult to interpret. Published demographic data on canine leptospirosis is limited. 

In addition, leptospirosis vaccines have the (probably justified) reputation of causing acute post-vaccination reactions, especially in small breeds. While current vaccines are generally regarded as protecting dogs from clinical illness subsequent to infection, they do not necessarily prevent infection or shedding of infectious spirochetes.

Conclusion

Today there is simply no room for complacency with respect to developing a rational vaccination protocol. 

It’s a fact: There are too many vaccines, too many issues and too much new information to ignore the changes affecting the selection and use of vaccines. 

The pace of change regarding vaccine technology along with new product introductions virtually mandate that veterinarians carefully assess the manner in which vaccines are selected and used in practice. The canine and feline vaccine guidelines represent an important educational resource for any veterinarian who administers vaccines to dogs and cats. 

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Dr. Ford, DVM, Dipl. ACVIM, (Hon) ACVPM, is a professor of medicine at North Carolina State University College of Veterinary Medicine.