How Vaccines Work
My-Dog.info > Dog Diseases, Bites, Worms & Ticks
Why does your pet need a set of boosters when beginning a
vaccination program? Doesn't a single "shot" work? How
do vaccines work to protect your pet from illness?
Clients often ask these and similar questions about the
life-saving vaccines we recommend. It is helpful to learn the
basic mechanism of how they (vaccines) do their job so that there
is a clear understanding of the strengths and limitations of
vaccines.
The study of vaccines is called vaccinology. Researchers
carefully produce test vaccines to help define the way they
produce immunity in the host (in this case, your dog or cat).
These intensive studies provide the basis for commercial vaccine
production. Extensive testing for efficacy (effectiveness) and
safety is carried out before the vaccine is licensed.
Some vaccines contain either whole viruses or bacteria that
have been treated to "weaken" them significantly. These
are term MODIFIED LIVE vaccines. Another vaccine class is
manufactured by killing the disease agent. Sometimes an adjuvant
(a component to make the vaccine more reactive in the system) is
added. These are termed KILLED vaccines. Many newer vaccines are
SUBUNIT vaccines. These vaccines are manufactured by extracting
components of the disease agent that normally act to stimulate a
response in a host (antigenic moiety). New genetic technologies
provide an even higher level of safety in vaccines. Selecting
only specific key components for inclusion into the vaccine
enhances their safety by eliminating unwanted parts of the agent
(such as certain cell wall components) that produce common
vaccine side effects such as fevers.
When a foreign agent enters the body, the immune system
rallies and sends sentry cells to protect the fort. If a novel
agent is identified, a complex series of events ensues that
results in the production of antibodies or cell-based immune
responses. In the immune system, cells are educated to recognize
these new foreigners, and remember the important response
information (memory cells). It is the memory cells that provide
the key to long-term vaccine-induced protection against these
agents. Memory cells may keep their programming for many years.
Natural infections and vaccines both produce protective reactions
in the body.
Immunity to a disease depends on a functional immune system.
Animals under significant stress, such that their system defense
is "tied up" doing other work, or is weakened to the
point of not being able to muster the forces will not develop
full immunity, even if the vaccine is fully potent. Sometimes
also, in very young puppies and kittens, the maternal antibodies
that their mother passes on to them interfere with the response
to the vaccine, and so boosters are given until the maternal
interference naturally degenerates. The youngster is then capable
of a full immune response. Because youngsters lose the protection
of the mother's transferred antibodies at different ages, the
vaccines are given so that the schedule covers the timeframe from
earliest to latest age of maternal protection loss.
Boosters are essential for most vaccines because the proper
education of these memory cells requires the presentation of the
offending foreigner more than once. This "anamnestic"
response is a learned programmed reactivity, and one-time
exposure may sometimes not be enough to trigger memory.
Note that vaccines are produced against the most common types
of disease agents. Within a family of bacteria or viruses,
variants can be present, or may emerge by the process of genetic
mutation. For this reason, new disease types may emerge and
vaccines may need to be adjusted to cover the animal against a
new subtype of the agent.
An important thing to remember is that the animal is not
considered fully vaccinated until ALL of the booster series is
complete + 2 weeks. It takes 10-14 days following the vaccine
administration in order to complete a full response.
No vaccine is 100% effective due to the reasons given above,
and others. Even so, most are very close to it, and the horrible
illnesses they prevent are much less common now thanks to the
widespread acceptance by owners of the vaccination
recommendations given by their health care team. Though vaccines
can produce side effects, when they are administered to reflect
the risk and lifestyle of each patient, the probability of side
effects is low indeed. Their cost is also miniscule when compared
to the cost of treating a case of one of the preventable, severe
diseases we protect against. The pet population is fortunate
indeed in these modern times because of excellent control of
epidemics by vaccination and hygiene that in past times, lead to
widespread death and serious illness.
Reprinted with permission from www.animalhealthcare.ca
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