Vaccines are a central player in our fight against infectious diseases. What components are commonly found in vaccines, and what is their purpose? In this Special Feature article, we find out.
Many
people will be familiar with the concept that a vaccine against a particular
virus will contain a small amount of the pathogen or a part of it, at least.
When
we receive the vaccine, the viral interloper triggers our immune system to
launch a series of events that leave us protected against the pathogen in the
future.
But
a glance at the ingredients in common vaccines reveals a long list of other
components, the roles of which might not seem so clear cut.
What
is the purpose of the likes of gelatin, thimerosal, and Polysorbate 80? And why
do some vaccines contain aluminum?
In
this Special Feature article, we look at the active and inactive ingredients
that make their way into vaccines and reveal what their role is in protecting
us from infectious diseases.
Our immune system and
active ingredients
The
active ingredient in a vaccine is usually made from the viral or bacterial
pathogen itself. There are two different approaches to this, with the
pathogen being either alive or inactivated.
Vaccines
that incorporate living bacteria or viruses are called live attenuated
vaccines. The pathogen is weakened to prevent it from causing the disease, but
it is still able to elicit a strong immune response.
Live
attenuated vaccines work very well, but they are not suitable for everyone. If
a person is immunocompromised, they may contract the very disease from which
the vaccine should be protecting them.
Many
vaccines, therefore, use an inactivated version of the active ingredients,
which can take the form of whole bacteria or viruses that have been killed.
However,
most vaccines are actually acellular, which means that they do not contain the
whole pathogenic organism. Instead, they are made from parts of the pathogen,
such as proteins or sugar molecules. Our bodies recognize these molecules as
foreign and mount an immune response.
Examples
of acellular vaccines are:
- toxoid vaccines that contain inactivated toxins from
pathogenic bacteria
- conjugate vaccines made from a combination of
pathogen-specific sugar molecules and toxoid proteins, as the sugars
themselves do not cause sufficiently strong immune responses
- recombinant vaccines made by using bacteria or yeast
cells to make many copies of specific molecules from the pathogen
Aside
from the active ingredient, vaccines contain many other things. The technical
term for these is excipients.
Excipients
include preservatives and stabilizers, traces of things that were used to
produce the vaccine, and adjuvants.
Adjuvants make vaccines
stronger
Although
many vaccines contain active ingredients that are strong enough to kick our
immune system into gear, some need a little bit of extra help to be effective.
Adjuvants
are compounds that elicit a strong immune response, improving how well a
vaccine works.
Examples
of adjuvants include:
- metals
- oils
- biological molecules, such as components isolated from
bacteria and synthetic DNA
Aluminum, in the form of aluminum salt,
features in a variety of vaccines, including several routine childhood
vaccines. Scientists believe that this adjuvant increases the production of
antibodies.
Aluminum
is a naturally occurring metal that has many uses aside from its adjuvant
properties. Cans, foil, and some window frames contain aluminum.
Aluminum
salts are also used in the food industry as additives.
As
an adjuvant, aluminum has a long history going back to the 1930s. Despite its widespread use, some scientists believe that the metal can cause damage to the nervous
system and promote autoimmunity.
However,
many experts disagree with this assessment, pointing out that some of the
research implicating aluminum has been retracted.
The
Food and Drug Administration (FDA) published a study in 2011 in the
journal Vaccine, which concluded that
“episodic exposures to vaccines that contain aluminum adjuvant continue to be
extremely low risk to infants and that the benefits of using vaccines
containing aluminum adjuvant outweigh any theoretical concerns.”
Another
example of an adjuvant is squalene, a naturally occurring oil.
The
Fluad vaccine, a flu vaccine
licensed for adults aged 65 years and older, contains an adjuvant called MF59,
which is an oil-in-water emulsion containing squalene. The squalene used in
MF59 is purified from shark liver oil.
In
2000, a research team pointed to a link between squalene and Gulf War
Syndrome, prompting fears about the safety of this adjuvant.
However,
subsequent research did not back up the findings,
and the World Health Organization (WHO) concluded
in 2006 that these fears were “unfounded.”
Source: Medical News Today
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