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Step 1
Use the tissue culture to grow new viruses.
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You are about to create a live-attenuated vaccine, which means that you need to
alter a pathogen—in this case a measles virus—so that it will still
invade cells in the body and use those cells to make many copies of itself,
just as would any other live virus. The altered virus must be similar enough to
the original measles virus to stimulate an immune response, but not so similar
that it brings on the disease itself.
To create a new strain of the virus, you'll need to let it grow in a tissue
culture.
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Step 2
Fill the syringe with a strain of the virus that has desirable characteristics.
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The tissue culture is an artificial growth medium for the virus. You will
intentionally make the environment of the culture different than that of the
natural human environment. For this vaccine, you'll keep the culture at a lower
temperature.
Over time, the virus will evolve into strains that grow better in the lower
temperature. Strains that grow especially well in this cooler environment are
selected and allowed to evolve into new strains. These strains are more likely
to have a difficult time growing in the warmer environment of the human body.
After many generations, a strain is selected that grows slow enough in humans
to allow the immune system to eliminate it before it spreads.
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Done
The measles vaccine is complete.
Select another pathogen.
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Congratulations. You have just produced a live-attenuated measles
vaccine.
Like the smallpox vaccine, the virus within the vaccine will invade body cells,
multiply within the cells, then spread to other body cells. The virus used in
the measles vaccine today took almost ten years to create. The starting stock
for the virus originated from a virus living in a child in 1954.
Live-attenuated vaccines are also used to protect the body against mumps,
rubella, polio, and yellow fever.
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