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 so they can prevent the vaccinia virus from spreading.
The vaccine can occasionally cause serious complications, such as infections affecting the heart or brain. That's why a general vaccination program for everyone isn't recommended at this time.
To learn more you should go to a medical professional.
Keyword: smallpox vaccination; smallpox vaccine