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[NARRATOR:] When you are infected with a virus like
SARS-CoV-2, your body gets to work destroying the virus.
Your immune system recognizes certain viral proteins,
called antigens.
Antigens trigger a process called the immune response
which includes the production of many types of immune cells
with different roles.
For simplicity, we will focus on B cells.
B cells produce antibodies
that bind to antigens.
When antibodies bind to antigens on a virus,
they can keep the virus from infecting other cells
and target the virus for destruction by the body.
Even after the virus is gone,
some B cells that recognize the virus
may stay in your body for years and protect you
from that virus in the future.
These are called memory B cells.
If you haven't come into contact with a particular virus before,
it can take weeks for your immune system
to produce enough antibodies to fight the unfamiliar virus.
In the meantime, the virus can cause serious disease
and spread to other people.
Vaccines help prevent disease caused by a virus that
is unfamiliar to the body.
A vaccine delivers antigens into your body
to trigger an immune response without causing disease.
Then if you are infected with the real virus in the future,
you already have B cells and antibodies to quickly
get rid of the virus.
Vaccines against SARS-CoV-2 and other viruses
deliver the viral antigens in three main forms:
as inactive whole virus, as antigen proteins,
or through genetic instructions.
Some vaccines deliver the whole virus,
which has been weakened or inactivated.
These viruses don't cause disease,
but still contain antigens that trigger an immune response.
Other vaccines deliver only the antigen.
In the case of SARS-CoV-2, some vaccines
deliver the spike protein.
These spike proteins are produced in the lab.
And other types of vaccines deliver
the genetic instructions, DNA or RNA, for making the antigens.
In the case of SARS-CoV-2, some vaccines
deliver a messenger RNA (or mRNA)
that encodes the spike protein.
The mRNA is delivered inside an artificial membrane
similar to the cell membrane.
When the mRNA enters one of your cells,
the cell's ribosomes translate the mRNA
into the spike protein antigen, which
triggers an immune response.
Other SARS-CoV-2 vaccines deliver spike protein DNA
instead of RNA.
The DNA is typically delivered using
an inactivated adenovirus: a modified virus that
can't multiply or cause disease, but can
bring the DNA into your cells.
Your cells then transcribe the DNA into mRNA,
which is then translated into spike proteins.
All these types of vaccines help the immune system
to develop an immune response against a virus
without causing disease.
The different parts of each vaccine --
such as inactive whole virus, antigens, mRNA or DNA,
and molecules that help with delivery --
are eliminated from the body.
But some of the memory B cells that
produce antibodies against the virus may last for years
and provide protection from the virus.
Sometimes another dose of a vaccine, called a booster shot,
is needed to keep levels of antibodies high.
And, over time, if the virus mutates,
you might need a new vaccine that delivers antigens matching
those of the mutated virus.
As more individuals in a community
get vaccinated and have antibodies to destroy a virus,
it becomes harder for the virus to spread among people.
So, getting a vaccine can help keep you, and those around you,
safe from disease.