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Smallpox was a naturally occurring disease that killed an estimated 300 million people in the 20th century. Its scientific name is Variola major, a virus from the Orthpoxvirus family. It was officially eradicated in the 1980, but has recently become a potential bioterrorism threat.


People can become exposed to smallpox by:

  • Prolonged face-to-face contact with someone who has the virus and is ill with fever and a rash of round lesions. (Typically, people with smallpox are not contagious until lesions start appearing and they are obviously ill.)
  • Direct contact with infected bodily fluids or an object such as bedding or clothing that has the virus on it.
  • The virus can also be used as a weapon and disseminated into the air as a fine spray or powder that could affect large numbers of people.


For the first 7 to 17 days after exposure, the infected person may feel fine and not be contagious. After the incubation period (7 to 17 days) the first symptoms begin to appear. The initial symptoms include fever, fatigue, head and body aches, and sometimes vomiting. The fever is usually high, in the range of 101 to 104 degrees Fahrenheit. This stage may last for 2 to 4 days.

Two to three days after the onset of symptoms, a rash appears first as small red spots on the tongue and in the mouth. A rash then appears on the skin, starting on the face and spreading to the arms and legs and then to the hands and feet. Usually the rash spreads to all parts of the body within 24 hours.

Seven days after the onset of the symptoms, the rash becomes raised bumps and the bumps become "pustules," which are raised, usually round and firm to the touch as if there's a small round object under the skin.

Twelve days after the symptoms, the pustules begin to form a crust and then scab. Severe abdominal pain and delirium can also occur in this later stage of the disease.

Three to four weeks after the onset of symptoms, scabs develop and fall off, leaving scars. A patient who survives is no longer contagious after the scabs fall off.


There is no proven cure for smallpox, so there is very little that physicians can do except provide supportive care. Patients with smallpox may be helped by intravenous fluids, medicine to control fever or pain, and antibiotics for any secondary bacterial infections that may occur.

One of the best ways to prevent smallpox is through vaccination. If given to a person before exposure to smallpox, the vaccine can completely protect them. Vaccination within three days after exposure will prevent or lessen the severity of smallpox in most people. Vaccination 4 to 7 days after exposure likely offers some protection from disease or may decrease the severity of disease. Vaccination will not protect smallpox patients who already have rash.

Currently, the smallpox vaccine is not widely available to the general public. However, there is enough smallpox vaccine to vaccinate every person in the United States in the event of a smallpox emergency.

For more extensive information about these agents, please visit Centers for Disease Control and Prevention.

Page last updated: May 13, 2021