Variola vaccinia, commonly known as smallpox vaccine, is a live-virus vaccine used to protect against smallpox. Synonyms for variola vaccinia include the vaccinia virus, cowpox virus, and the smallpox virus. The vaccine uses live virus to create an immune response in the body, which prepares the immune system to fight off the smallpox virus in case of exposure. Variola vaccinia was first developed in the late 18th century and has been used to eradicate smallpox worldwide. Today, the vaccine is primarily used by military personnel and healthcare workers who may be exposed to the virus in the line of duty.