All Pets Veterinary Clinic


Vaccines have long been known to be a beneficial part of the overall preventative
health strategy for animals and humans. However, vaccines and traditional vaccination
protocols have recently come under fire as people question if the risks of vaccines
are worth the benefits that they provide. The remainder of this article will review
what vaccines are, how they work, the benefits and risks of vaccination, the vaccine
controversy, and recommendations for vaccination. Please note that this article
is not intended to dictate a vaccination protocol for your pets but to help you, the
pet owner, become more aware of the issues at hand.

What Are Vaccines?
Vaccines are made of whole organisms or portions of organisms (typically bacteria or
viruses) that can cause disease. Vaccinations may also contain some sort of adjuvant
or carrier and preservative. Vaccines can protect against single organisms, as with a
rabies vaccination, or multiple organisms, as with a distemper vaccine. Vaccines are not
available for every organism that causes disease. There are many diseases that do not
have vaccinations available.

How Vaccines Work
Stated simply, when a vaccine is given to an animal it stimulates the immune system
to make antibodies. These antibodies are specific for whatever organism the vaccine
is protecting against. The antibodies are then "stored" for future use. If the
animal becomes exposed to an organism that it has been previously vaccinated for
the antibodies will help prevent or minimize illness.

The Benefits of Vaccination
The major benefit of vaccination is the prevention of disease or in some instances, the
lessening of the severity of illness. For the single animal the significance is obvious.
Protecting our pets from undo disease or illness is important. On a larger scale, disease
prevention in large groups of animals, especially our food producing species, such as
cattle or hogs, is critical. If one animal in a herd becomes sick with a disease that
the herd is not vaccinated for the outcome can be economically devestating. Massive
illness and loss can occur. Another potential benefit of vaccination is to prevent
human illness. There are several diseases that animals can transmit to people (i.e.
zoonotic diseases). Some include Rabies, Salmonella, and Ringworm. If the animals
that can spread these diseases to people are vaccinated then we (humans) get some
protection against illness as well.

Potential Side Effects
Vaccines are drugs and like any drug, they can have side effects. The most common
side effects are lethargy, pain at the site of injection, and swelling at the site
of injection. These side effects are typically short-lived, often lasting less than
24-48 hours, and mild. More serious side effects can include allergic reaction,
autoimmune hemolytic anemia and vaccine induced fibrosarcoma, an aggressive tumor.
These side effects can vary from mild to severe and are less likely to occur. For
example, the rate of vaccine induced fibrosarcoma is between 1 in 10,000 and 1 in
100,000 vaccinated cats.

The Vaccine Opponents
Given the potential severity of some of the side effects of vaccination and the perception
that some of the diseases we vaccinate for are rare or unseen, some people believe that
vaccination is no longer necessary. This may or may not be true. Perhaps the reason
that we do not see the diseases that we vaccinate for is that we have done a good job
preventing them through aggressive vaccination protocols. Two examples of this theory
can be demonstrated here. First, consider parvovirus. Parvo was a major killer of
dogs when it first became widespread in the seventies. Since it was a new virus, dogs
had no protection and became ill when exposed. When a vaccine was developed and used,
the numbers of animals becoming ill declined because they were given advanced protection
against the virus. Today, we still see parvo but not nearly as often as we used to.
The animals that become infected with parvo are most commonly animals that have not
been vaccinated. Secondly, consider West Nile Virus, a modern day virus that is new
to the United States (first found in the US in 1999). In these, early years of the
virus many birds, horses, and people are exposed and become ill because they do not
have protection against the virus. A vaccine has been developed and is currently
available for use in horses. As more and more horses are vaccinated, fewer will become
ill with the virus. As vaccination increases, new cases of West Nile Virus in horses
will become less common. Hopefully, a vaccine for humans will become available as well.

Alternative Recommendations
Another group recognizes the benefits of vaccinations but suggests that vaccines may
protect against disease for extended periods of time. Currently, most vaccinations in
veterinary medicine are readministered annually. Rabies vaccines may be the exception,
with every third year revaccination, but this depends on state and county laws. The
annual revaccination period is based on vaccine manufacturer recommendations. Most
vaccine companies recommend annual revaccination of their products based on initial
tests done for FDA approval. The problem with these initial tests is that they did
not include studies to determine how long the vaccine lasted. Therefore, this information
is largely unknown. A few smaller studies have, however, suggested that some
vaccinations last longer than one year. Thus, this group is recommending every third
year vaccination.

There may be a few problems with this recommendation. First, there are no large, long term
studies that state exactly how long these vaccines last. Some animals may have protection
for shorter or longer than three years. For animals with shorter immunity they may
be left unprotected with every third year vaccination. Secondly, three year vaccination
protocols will not eliminate side effects of vaccinations. Regardless of the length
between vaccination, some animals will still have vaccine related side effects.

Duration of Immunity
Duration of immunity is at the heart of the vaccine controversy. Duration of immunity
simply means how long a given vaccination lasts. The biggest problem at this point in
time is that there are no reliable, definitive means to determine how long a given
vaccination provides protection. There have been attempts to quantify duration of
immunity through the use of titers. To determine a titer for a given vaccine, a blood
sample is necessary. When a titer is taken, a laboratory will provide a number
demonstrating immunity. This number is then compared to known protective levels and
protection can be determined. For example, if we want to know if a dog has protection
against a certain virus, a blood sample can be drawn and a titer can be run. Say the
lab determines the titer to be 1:4 and protection has been determined to be at a level
of 1:4. This would mean that the dog had adequate protection against the virus and
additional vaccination is not necessary. Sounds easy, right? The problem with titers
is complex. First of all, lack of a titer does not always mean that the animal is not
protected. Second, titer technology is not available for all of the vaccines that are
offered. Third, in many cases there is not enough data available to determine what a
protective titer is. So, if an animal has a 1:20 titer that may or may not mean that
if an animal becomes infected with that pathogen that it will not become sick. Thus,
duration of immunity is an important part of the controversy. If we knew how long
vaccines lasted and had an accurate way to determine the level of protection, we would
not be having this discussion.

What Should You Do?
At this point in time, given the information that is available on vaccination, there
are several questions and concerns. First, what is the true rate of complications
from vaccines? In my experience, mild vaccine reactions (lethargy, soreness, etc.)
are fairly common and rarely fatal. In the eight years since I have graduated from
veterinary school I have seen two cases of vaccine induced fibrosarcoma and one case
of autoimmune hemolytic anemia. (i.e. these side effects have been very rare in my
expereince.) Second, if we decrease our frequency of vaccination will we increase
the number of cases of the diseases that we are vaccinating for? Third, how can we
easily and safely determine duration of immunity and be assured that the data is
correct and accurate? (i.e. if a titer tells us that the pet is protected, is it
really protected?)

Thus, given the current information, one should consider the risks and benefits of
vaccines in relationship to the individual pet. How at risk is the pet for the
diseases that we are vaccinating for? Typically, pets that are higher risk for disease
spend time outside, live in multipet households or have exposure to other animals,
and/or have a history of fighting with other animals. There are certainly other risk
factors and they vary by disease. How likely is the vaccine to cause side effects? This
is a difficult question as individuals vary greatly. Has the pet had side effects
from vaccination in the past? Is the pet healthy or does he/she have a history of
illness? Discuss these things with your veterinarian and come up with a reasonable
plan for each individual pet. Hopefully, with time additional studies and testing
methods will make the decision to vaccinate or not to vaccinate more clear cut.

The information provided is for educational purposes only and is not
intended to take the place of your regular veterinarian. Please do not hesitate
to contact your regular veterinarian if you have questions regarding your pet.

Karen Blakeley, DVM, MPH
1 September 2005