New Approach to Vaccination of the Canine
by Leanne Bertani, MD
For years, it was believed that annual vaccinations for viral diseases were
necessary to keep our beloved companions out of harm's way. But we have
recently come to a turning point in vaccination of the canine. While we are
greatful for protection from diseases such as distemper and parvovirus,
there is growing realization that vaccination is not always benign.
In 1996, a study was published suggesting an association between
vaccination and autoimmune disease, specifically autoimmune hemolytic
anemia, an often fatal destruction of red blood cells.(1) This was followed
by another study that demonstrated that dogs may develop an autoimmune
response after vaccination.(2) In 1998, the American Association of Feline
Practitioners responded to the increasing incidence of vaccine-induced
fibrosarcomas in cats by changing the recommendation for feline parvovirus
vaccination from annually to every three years.
These events, coupled with the knowledge that some vaccinations for viral
diseases may protect for seven or more years, have caused veterinarians and
dog breeders alike to begin to ask, "Are we vaccinating too much?"
Duration of Immunity for Common Vaccines
Studies have shown that, once fully immunized, more than 90% of canines
retain immunity to Parvovirus-2 and Adenovirus-2 for more than seven years.
(Full immunization may not take place with vaccinations administered prior
to 16 weeks, due to interference by maternal antibodies.) Immunization to
Distemper may last up to 15 years, and immunization to Coronavirus probably
lasts a lifetime. Immunization to Rabies and Parainfluenza lasts about 3
years in about 80-85% of dogs. Note that proven duration of immunity may
vary dependent on the type of vaccination used; for instance, modified live
parvovirus demonstrated a longer duration of immunity than killed virus; one
strain of distemper tested for a longer duration than another. New
recombinant vaccines may be more efficient and produce a longer-lasting
immunity.
Other vaccines, particularly the bacterial ones, are less durable. Some
vaccines to Bordetella may last less than a year and are probably only
effective in about 70% of dogs. Sufficient data on Leptospira, Borrelia
(Lyme) and Giardia vaccine is not available to suggest immunization lasting
much longer than a year.(4)
Progress in the Veterinary Community
The American Veterinary Medical Association Council on Biologic and
Therapeutic Agents published immunization recommendations for dogs and cats
in 1989, suggesting annual revaccination. The companies that produce the
vaccines also suggest annual revaccination. A study published in 1998 found
that 27% of vaccinated dogs had a less-than-protective CPV titer, and 21% of
dogs had a less-than-protective CDV titer, and summarized that the current
practice of annual revaccination of dogs against CPV and CDV infection
should be maintained. (5) (Critics of that study argue that authors used
CDV antibody titers that are inconsistent with sterilizing immunity and
don't take into consideration that those dogs with lower titers will be
protected from disease but not infection.)
With the above in mind, it was understandable that veterinarians were
reluctant to buck tradition, as the legal community generally compares
medical practice to the "standard of care".
But the vaccination revolution received a couple big pushes in 2001. The
January 2001 issue of The Veterinary Clinics of North America (Small Animal
Practice) featured vaccinations and discussed the need for reconsidering
traditional annual vaccinations. A chapter author, Dr. Ronald Schultz,
Professor & Chair at the University of Wisconsin, says that their Veterinary
Medical Teaching Hospital has been on an "every three or more" year
vaccination schedule for cats and dogs for over four years. "The goal for
the future should be to vaccinate more animals than are now vaccinated but
to vaccinate those animals less often and only with the products that the
animal needs," says Dr. Schultz.
Another advance came in April 2001, when the American Veterinary Medical
Association Executive Board approved the Council on Biological Therapeutics
new "Principles of Vaccination." This statement was published in the
Journal of the American Veterinary Medical Association on September 1, 2001.
The principles state that "unnecessary stimulation of the immune system does
not result in enhanced disease resistance and may increase the risk of
adverse post-vaccination events." It recommended that veterinarians create
"core" and "non-core" vaccination programs (see below for examples), and
that vaccine schedules be tailored to the needs of each specific animal.
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