vaccines have an important role in
protecting us
from infectious disease but how do they
work
well put simply vaccines train our
immune system to detect
and attack pathogens and we're going to
walk you through how they do it
from start to finish our immune system
is a marvelously complex network of
molecules and cells
which has the power to destroy pathogens
like viruses and bacteria
the part of the immune system that
vaccines train is called the adaptive
immune system
its first job is to recognize an invader
in the case of this bacterium it does
this by detecting molecular markers
called antigens that are part of all
pathogens
after detecting an antigen the adaptive
part of the immune system
starts mounting a bespoke response
b cells convert to plasma cells and
start creating proteins called
antibodies
which bind specifically to the antigen
together with immune cells called
phagocytes
antibodies can destroy the pathogen
the adaptive immune system also produces
killer t
cells which have the ability to detect
and destroy
cells infected with the pathogen but it
doesn't end there
to prevent against future infections the
adaptive immune system
also has a memory it produces long-lived
memory cells which lie in weight ready
to pump out the right antibodies and
killer t cells
if the same pathogen is ever seen again
this is called immunity vaccines work
by activating the adaptive immune system
and so
creating immunity they safely introduce
antigens
for the immune system to train on
preparing itself to fight
real infections in the future so what
actually goes
into a vaccine well there are several
different types
one of the most common are called live
attenuated vaccines
these include things like mmr or bcg
live attenuated vaccines work by
introducing a weakened version of a
living pathogen
into the body these attenuated pathogens
are not strong enough to cause disease
in people with healthy immune systems
but they can still trigger a strong
immune response
live attenuated vaccines trigger a
similar immune response to a real
infection
leaving behind the same memory cells
this means that some can provide a
lifetime of protection after just one or
two doses
another key type of vaccine is called a
subunit or recombinant vaccine
they work differently instead of a live
sample
subunit vaccines contain only part of
the pathogen
for instance the vaccine for human
papilloma virus
hpv uses hollow virus-like particles
made from a protein
found in hpv
alone these subunits cannot get the
immune system's attention
and so they need a bit of help from
another ingredient
an adjuvant adjuvants wake up the immune
system
triggering it to see the subunit
antigens and start creating antibodies
and memory cells
subunit vaccines contain no life
pathogens
and so lack the genetic information
needed to replicate
that means they are not infectious and
are safe even for people with weakened
immune systems
great but generally they don't trigger
the production of as many memory cells
compared to live attenuated vaccines and
so
they don't provide such long lasting
protection
training the immune system through
vaccination helps to protect
individuals from infection but vaccines
can also protect people who can't
receive them
this is called herd protection or herd
immunity
herd immunity is created when a large
percentage of a population
is immune to a disease it works by
disrupting
chains of infection without new hosts to
infect
pathogens can't survive that means that
if a pathogen tries to infect someone
who is vaccinated
and so immune it dies and the chain of
infection
is broken if enough chains are broken in
a population
it becomes very difficult for pathogens
to reach those who would be vulnerable
herd immunity protects millions of
people around the world
but if vaccination rates drop there is a
risk the diseases
can reappear for example measles was
declared eradicated in the united states
in 2000
but since then falling vaccination rates
have led to a resurgence of the disease
with outbreaks recorded
in 31 states if herd immunity is
maintained
for long enough though diseases can be
eradicated completely
for example smallpox which is estimated
to have killed
300 million people in the 20th century
is now considered
extinct all thanks to vaccination
its training regime and the wonders of
herd immunity
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