Smallpox is a contagious viral illness caused by the variola virus. The virus can spread from an infected person through the air when there is fairly prolonged (1-3 hours) direct contact. It can also spread via body fluids, either by direct contact with fluids from an infected person or by touching objects that have been contaminated by infected body fluids. The last documented case of smallpox disease occurred in 1977. However, smallpox is still considered a possible biological threat.
An infected person usually begins to experience symptoms 12 to 14 days after exposure. Smallpox disease results in a fever and viral-like symptoms, followed by a rash that progresses from papules to pustules. Eventually the pustules form scabs and the scabs fall off. People with smallpox can spread the virus to others beginning when their fever is 101°F until all their scabs fall off.
There is no proven cure for smallpox. Historically, death has occurred in about 30% of cases. Giving smallpox vaccine soon after exposure to the virus can help to reduce the effects of smallpox disease. Vaccine given within 3 days after exposure can help prevent death. Vaccine given within 7 days after exposure can result in a less severe (modified-type) smallpox illness.
There is only one smallpox vaccine available in the United States. It is a live, attenuated vaccine made from vaccinia virus. Vaccinia virus is closely related to variola virus, which is the virus that causes smallpox. Immunity against vaccinia virus also provides protection against variola virus. It is administered using a bifurcated needle that is jabbed into the surface of the skin.
To reduce the chance of spreading the vaccine virus to other body parts or other people, please follow these recommendations:
Smallpox vaccine contains live vaccinia virus (not smallpox virus) to protect against smallpox. This same vaccine has been given to millions of Americans, including Service members during World War I, World War II, and until the 1980s. Between December 2002 and January 2008, more than 1.4 Million Service members received smallpox vaccination.
The vaccine is made from a virus called vaccinia, which is another "pox"-type virus related to smallpox. The vaccine helps the body develop immunity to smallpox. The vaccine does not contain the smallpox virus and cannot spread smallpox. The vaccine was successfully used to eradicate smallpox from the human population.
The vaccine virus (vaccinia) is similar to the smallpox virus (variola). Edward Jenner reported in 1796 that people given vaccinia (smallpox) vaccine become protected from smallpox. Smallpox vaccine was the very first vaccine and has been used successfully for over 200 years.
Getting smallpox vaccine before exposure will protect about 95 percent of people from getting smallpox. Vaccination within 3 days after exposure will prevent or significantly lessen the severity of smallpox symptoms in the vast majority of people. Vaccination 4 to 7 days after exposure likely offers some protection from disease or may modify the severity of disease. Vaccination after this time may not offer any benefit.