Smallpox is a serious, contagious, and sometimes fatal infectious disease caused by a virus called the variola virus. The disease gets its name from the Latin word for “spotted” and refers to the small pus-filled blisters that appear on the face and body of an infected person.

Why has smallpox been in the news?

Although smallpox has been eradicated, there is growing concern that terrorists might obtain the smallpox virus and unleash it in a bioterrorist attack.

What are the symptoms of smallpox?

People infected with smallpox develop some symptoms (for example, fever, headache, backache, and general fatigue) that are typical of many less serious diseases. However, the telltale sign is the development of a unique skin rash. The rash, which has an indentation (hollow area) at its center, covers the entire body. The rash progresses to a raised bump, then to a pus-filled blister that crusts and scabs over before finally falling off about three weeks later, leaving behind a pitted scar.

How long does it take smallpox symptoms to appear?

After exposure, there's a period of seven to 17 days (called the incubation period) during which an infected person may not show any symptoms. Then, over the next two to four days, an infected person may become sick with cold and flu-like symptoms (this is called the prodromal stage). The classic smallpox rash begins after these cold and flu symptoms disappear. So, the earliest outward symptoms of smallpox would appear about nine days after exposure, when the rash develops.

A person with smallpox is most contagious to others while the rash is present, but is still considered contagious until the last smallpox scab falls off. A person is not contagious during the incubation period, and only sometimes contagious during the prodromal stage.

How is smallpox spread?

Smallpox is spread from person to person by several means, including:

  • Direct, face-to-face, and fairly prolonged contact with an infected person. For instance, the saliva of the infected person can spread the disease.
  • Direct contact with the fluid in the blisters in the infected person's skin or other infected bodily fluids
  • Direct contact with contaminated objects, such as blankets, towels or clothes touched by an infected person

Smallpox is rarely spread through the air in settings such as buses, trains, or office buildings.

Is smallpox fatal?

About 30 percent of people who become infected with smallpox die from their illness.

How is smallpox treated?

There are no drugs to treat smallpox once a person develops the disease. (Drugs can be given to relieve some of the cold and flu symptoms and other illnesses that might arise in addition to the smallpox.) Instead, a vaccine is given to prevent people from contracting the disease in the first place.

Currently, only military personnel who might be exposed to smallpox as a biological weapon of warfare and U.S. healthcare workers ("first responders") are offered the vaccine. However, enough vaccine has been manufactured to inoculate every man, woman, and child in the United States should a bioterrorist attack with smallpox occur.

If there is an outbreak of smallpox, vaccination within three days of exposure will completely prevent or significantly modify the severity of disease in most patients. Vaccination within four to seven days of exposure will likely offer some protection against the disease. The vaccine provides protection from smallpox for three to five years.

How is the smallpox vaccine given?

A bifurcated (two-pronged) needle that has been dipped into the vaccine solution is used to prick the skin of the upper arm several times. The pricking is not deep, but will cause a sore spot and one or two droplets of blood to form. If the vaccination is successful, red, itchy bumps develop at the vaccination site. This is followed a few days later by a blister, and finally a scab that falls off about three weeks later.

Is the smallpox vaccine safe?

The smallpox vaccine offers the best protection against contracting the smallpox virus, which can be fatal. The vaccine is not without some risks, however. Based on the history of smallpox vaccination:

  • Between 14 and 52 people per one million vaccinated will have a potentially life-threatening reaction.
  • One to two of these people will die from these reactions.
  • About 1,000 people per one million vaccinated will have serious but not life-threatening reactions.

It is important to note that smallpox cannot be contracted from the vaccine.

In the spring of 2003, several people who received the vaccine suffered heart attacks and died. The Centers for Disease Control and Prevention (CDC) is conducting an investigation to determine if there is any association between smallpox vaccination and the development of heart problems. The government agency recommends that anyone with a history of heart disease, or who is suffering from three or more major risk factors for heart disease, be excluded from the vaccination program. Risk factors for heart disease include diabetes, high blood pressure, high cholesterol levels, and smoking.


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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 1/17/2017...#10855