A vaccine used to provide immunity against smallpox, one of the deadliest infections in the history of humanity. The vaccine is made from live vaccinia virus (not from the smallpox virus ). Similarities between the two viruses make the vaccine about 95% effective in preventing smallpox in those people exposed to the virus. Smallpox vaccine was not used for many years because smallpox had been eradicated worldwide. However, concerns over the use of smallpox as a biological weapon have resulted in vaccination of persons at high risk (e.g., public health workers, health care response teams, members of the armed services). The general public is not being vaccinated. The CDC recommends that persons who could be exposed to the monkeypox virus should also be vaccinated against smallpox.