Figure 2-1. Geographical areas requiring specific immunizations.
IMMUNITY AND RESISTANCE
A susceptible or nonimmune has little resistance against a particular disease
organism and, if exposed to it, is liable to contract the disease. By contrast, an immune
has a high degree of resistance to the organism and, when exposed, does not develop
the disease. While most babies are born with a high level of immunity to many disease
organisms, this immunity is lost within a few months. The immunity possessed by
adults usually is acquired either naturally or artificially after birth and may be temporary
or permanent. The basic component of immunity or specific resistance is the antibody.
Antibodies are proteins produced by the body system in response to stimulation by a
foreign substance (antigen) and having the capacity for combining specifically with that
substance. Immunization may be active or passive.
a. Active. In active immunization, antibodies are formed within the body
because of the presence of the natural infection (natural immunity) or because of the
inoculation into the body of infectious agents or antigenic substances derived there from
(artificial immunity). In active immunity, a physical change is effected which is relatively
slow in developing (10 to 114 days), but whereby a permanent immune pattern is
created. While the level of active immunity may decline over a period of years, it is
susceptible to stimulation and elevation by a relatively small amount of immunizing
material. The immunizing material comprising the vaccine that is inoculated may be
either weakened (attenuated) or killed (inactivated) disease organisms or their products.