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Let's talk about immunity.
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Immunity allows us to tolerate the presence of an agent,
such as a bacteria or virus.
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It's our ability to resist infection. There are several
types of immunity that prevent infectious disease.
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So let's talk about those different types.
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First, we have passive immunity.
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Passive immunity occurs when a person is given immunity.
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Now, this is short-term immunity that provides resistance to
a specific disease-causing agent.
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There are two different ways that one can be given immunity.
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One is through maternal antibody transfer.
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This is the transfer of antibodies from a mother to a
newborn.
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It can take place in two different ways, through the
placenta or through breastmilk.
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So, in this instance, it's like the newborn is borrowing
immunity from the mother.
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The second way that one can be given passive immunity is
through receiving immunoglobulin therapy.
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This means transferring immunity through the administration
of immunoglobulin in a healthcare facility.
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So, let's say for example someone's bitten by a venomous
snake. They receive antivenom.
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So, let's say for example someone's bitten by a venomous
snake. They receive antivenom.
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This is really just a combination of antibodies against that
snake's venom.
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The best part about passive immunity is that it's immediate.
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However, it only lasts for a short period of time.
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The second type of immunity is active immunity.
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Active immunity is a result of production of antibodies in
our immune system
as a result of exposure to an infectious agent.
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Active immunity is long-term immunity.
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It can be acquired either naturally, through infection with
the actual disease,
or artificially, through vaccination against the disease.
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Either way, this type of immunity occurs as a result of an
exposure to disease organism.
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This exposure triggers the immune system to produce
antibodies
to that disease in the moment, and in the future.
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Then we have herd immunity.
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Herd immunity is also sometimes called community immunity.
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This is the level of immunity required to resist a
particular disease in a specific population.
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Now, in this image, we have the peach population.
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They're non-immunized but still healthy.
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The red represents those who are non-immunized, sick, and
contagious.
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If herd immunity is low, meaning that few people in the
community are immune,
spread of disease is more likely.
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So, here, on the left, we see the majority of people in this
community are healthy,
but because they're not immunized, even just a few cases of
infection in the community
can result in high levels of community infection.
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But, also, recognize that those who are immunized and
healthy,
here, the green population, they remain healthy and not
contagious.
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On the other hand, once a large majority of the population
are vaccinated and are immune,
there's less opportunity for the spread of disease.
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Herd immunity protects the unvaccinated
and those with compromised immune systems from getting
infection.
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As I mentioned earlier, vaccinations are one way in which
people acquire active immunity.
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Vaccinations are cost-effective public health intervention
that have had an incredible impact on life-expectancy in the
20th century.
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There are a wide variety of diseases that are
vaccine-preventable.
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Some examples are hepatitis B, measles, influenza.
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There are also diseases such as polio that we've almost
forgotten about due to the impact of vaccines.
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Most vaccines are developed using either a live organism or
an inactivated form of the organism.
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Live attenuated vaccines are made from weakened virus
organisms
that can still replicate but are too weak to make a person
ill.
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This initiates an immune response and the individual builds
immunity against the virus for future exposure.
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Next, inactive vaccines, are made from viral organisms that
have been inactivated by either chemicals or by heat.
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The viruses in inactivated vaccines cannot replicate,
however, they initiate that immune response.