Terms Listed Alphabetically
Evolution of Vaccines
Over 200 years ago, English physician Edward Jenner
observed that milkmaids stricken with a viral
disease called cowpox were rarely victims of a
similar disease, smallpox. This observation led
to the development of the first vaccine. In an
experiment that was to prove a revelation, Jenner
took a few drops of fluid from a pustule of a
woman who had cowpox and injected the fluid into
a healthy young boy who had never had cowpox or
smallpox. Six weeks later, Jenner injected the
boy with fluid from a smallpox pustule, but the
boy remained free of the dreaded smallpox.
In those days, a million people
died from smallpox each year in Europe alone,
most of them children. Those who survived were
often left with grim reminders of their ordeals:
blindness, deep scars, and deformities. When Jenner
laid the foundation for modern vaccines in 1796,
he started on a course that would ease the suffering
of people around the world for centuries to come.
By the beginning of the 20th century, vaccines
for rabies, diphtheria, typhoid fever, and plague
were in use, in addition to the vaccine for smallpox.
By 1980, an updated version of Jenner’s
vaccine led to the total eradication of smallpox.
Since Jenner's time, vaccines have
been developed against more than 20 infectious
diseases such as influenza, pneumonia, whooping
cough, rubella, rabies, meningitis, and hepatitis
B. Due to tremendous advances in molecular biology,
scientists are using novel approaches to develop
vaccines against deadly diseases that still plague
Scientists use vaccines to “trick”
the human immune system into producing antibodies
or immune cells that protect against the real
disease-causing organism. Weakened microbes, killed
microbes, inactivated toxins, and purified proteins
or polysaccharides derived from microbes are the
most common components used in vaccine development
strategies. As science advances, researchers are
developing even better Vaccines ones.
Different Types of Vaccines
Weakened Microbes. Live microbes
are weakened by growing them for many generations
in animals or in tissue cultures in the laboratory.
These weakened microbes can be inoculated into
humans to provide protection from their disease-causing
counterparts. The oral polio vaccine, as well
as vaccines for mumps, measles, and rubella, have
been developed from weakened microbes. Experimental
vaccines for influenza and respiratory syncytial
virus (RSV) are being tested in clinical trials.
Killed Microbes. A number of vaccines
have been developed from whole organisms that
have been killed. These inactivated microbes (technically,
the vaccine isn’t inactive) do not cause
disease in people who receive them, but they can
stimulate the immune system. Such vaccines in
use today include those against polio and influenza.
Inactivated Toxins. Some bacteria
cause disease by producing toxins that invade
the bloodstream. Inactivated toxins have been
used successfully to prevent diseases such as
tetanus and diphtheria since the early 1900s.
Subunit Vaccines. Recent research
has focused on developing vaccines that use only
part of a bacterium or virus. These vaccines,
called subunit vaccines, produce an effective
immune response without stirring up separate and
potentially harmful immune reactions to the many
antigens carried on a microbe. Subunit vaccines
are currently available for typhoid and hepatitis
B. Acellular pertussis subunit vaccines have been
demonstrated to be effective in preventing whooping
cough in babies and young children. Although not
considered subunit vaccines, vaccine candidates
using only the outer polysaccharide coat of the
bacterium have been developed for meningitis and
Conjugate Vaccines. Bacterial diseases
such as pneumonia and meningitis once caused considerable
illness and death among babies and children in
the United States. Bacteria that cause these diseases
have an outer coat that cannot be recognized by
the immature immune systems of young infants and,
therefore, vaccines made from these bacteria are
not effective in babies. Researchers have devised
a way to produce vaccines that link together proteins
or inactivated toxins from a second organism to
the outer coat of the bacteria. This enables a
baby's immune system to respond to the combined
vaccine and produce antibodies, initiating an
immune response against the disease-causing organism.
The licensed conjugate vaccines against Haemophilus
influenzae type b (Hib), previously the major
cause of bacterial meningitis in babies and young
children, have virtually eliminated the disease
in the United States.
Vaccines Through Biotechnology
Advances in biotechnology are enabling
scientists to change the genetic structure of
infectious microbes for use in vaccine development.
In these so-called “recombinant” vaccines,
researchers alter an organism's genetic structure
by snipping out a key gene, thereby allowing the
organism to produce immunity but not disease.
In contrast, researchers can also insert a gene
into an organism's genetic material, causing it
to mass produce "foreign" proteins,
or antigens, which can be used to induce an immune
response. In another approach, DNA is removed
from an organism and modified so that it contains
only a fragment of the original genetic material.
Scientists theorize that when this "naked"
DNA is inoculated into humans, the body's own
cells will use it to generate antigens to protect
against disease. Such DNA vaccines could potentially
result in lifelong protection and are being tested
in humans against malaria, influenza, and HIV.
Genome Sequencing. Numerous projects
are under way to sequence the genetic instructions,
or genomes, of disease-causing microbes. NIH-supported
researchers have reported the complete genomic
sequence of several microbes including, including
group A streptococcous tuberculosis, and of the
malaria parasite Plasmodium falciparum. New genomic
sequence data provide important insights into
the components of these organisms that might be
incorporated into candidate vaccines.
Edible Vaccines. Researchers have
found that edible vaccines can safely and effectively
trigger an immune response against the Escherichia
coli bacterium and the Norwalk virus. Scientists
are now attempting to genetically engineer potatoes,
bananas, and tomatoes that, when eaten, will initiate
an immune response against harmful intestinal
bacteria and viruses.