The smallpox vaccine is used to help prevent this disease. This vaccine works by exposing you to a small dose of the virus, which causes the body to develop immunity to the disease. This vaccine will not treat an active infection that has already developed in the body. The smallpox vaccine contains live "vaccinia" virus (a virus similar to smallpox). For this reason, the vaccination site (the place on your skin where the vaccine is injected) will be contagious and can spread the virus to other parts of your body or to other people. Like any vaccine, the smallpox vaccine may not provide protection from disease in every person.