The vaccination against small pox means the introduction of
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weakened germs
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lymphocytes
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leucocytes
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antibodies
The smallpox vaccine protects people from smallpox by helping their bodies develop immunity to smallpox. The vaccine is made from a virus called vaccinia, which is a poxvirus similar to smallpox, but less harmful. The smallpox vaccine contains live vaccinia virus, not a killed or weakened virus like many other vaccines. For that reason, people who are vaccinated must take precautions when caring for the place on their arm where they were vaccinated, so they can prevent the vaccinia virus from spreading. The vaccine does not contain the smallpox virus and cannot give you smallpox. For most people with healthy immune systems, live virus vaccines are effective and safe. Smallpox vaccination can protect you from smallpox for about 3 to 5 years. After that time, its ability to protect you decreases. If you need long-term protection, you may need to get a booster vaccination.
So, the correct option is 'Weakened germs'.