Lec no 6(1)

Vaccines

Definition
A substance used to stimulate the production of antibodies and
provide immunity against one or several diseases, prepared from
the causative agent of a disease, its products, or a synthetic
substitute, treated to act as an antigen without inducing the disease.
A vaccine typically contains an agent that resembles a disease-
causing microorganism and is often made from weakened or killed
forms of the microbe, its toxins, or one of its surface proteins.

Types of vaccines
LIVE, ATTENUATED VACCINES
Live, attenuated vaccines contain a version of the living microbe that has
been weakened in the lab so it can’t cause disease. Because a live,
attenuated vaccine is the closest thing to a natural infection, these
vaccines are good “teachers” of the immune system. They elicit strong
cellular and antibody responses and often confer lifelong immunity with
only one or two doses.

Despite the advantages of live, attenuated vaccines, there are some
downsides. It is the nature of living things to change, or mutate, and
the organisms used in live, attenuated vaccines are no different. The
remote possibility exists that an attenuated microbe in the vaccine
could revert to a virulent form and cause disease. Also, not everyone
can safely receive live, attenuated vaccines. For their own
protection, people who have damaged or weakened immune
systems—because they’ve undergone chemotherapy or have HIV,
for example—cannot be given live vaccines.

Another limitation is that live, attenuated vaccines usually need to
be refrigerated to stay potent. If the vaccine needs to be shipped
overseas and stored by healthcare workers in developing countries
that lack widespread refrigeration, a live vaccine may not be the
best choice. Live, attenuated vaccines are relatively easy to create
for certain viruses. Vaccines against measles, mumps, and
chickenpox, for example, are made by this method.