Skip to main content


Smallpox is a reportable disease in Oklahoma. Smallpox is an acute infectious disease caused by the variola virus. The last naturally acquired case of smallpox occurred in 1977. Smallpox was declared eradicated from the earth in 1980. However, the events of September and October 2001 have emphasized the need to be prepared for a biologic attack using smallpox as a weapon.

The initial symptoms of smallpox include the acute onset of fever, chills, headache, nausea, vomiting, and severe muscle aches. This stage generally lasts for two to four days. By the fourth day of illness, the fever drops and the characteristic smallpox rash appears. The rash starts out flat or slightly thickened spots (known as macules) and quickly progresses to raised spots (known as papules). These papules continue to enlarge and become filled with a clear fluid (known as vesicles). The fluid in the vesicles gradually change from clear to pus-like, and the lesions are then referred to as pustules. During the pustule stage, a fever is common and the pustules start to form into scabs. Over time, the dried scab material falls off of the skin. This entire process takes three to four weeks, and the areas affected by the rash can be permanently scarred. Symptoms of smallpox occur within seven to 17 days after exposure.

There are two types of smallpox: variola major and variola minor. Variola major is the more severe form and has a 30 to 50 percent fatality rate among those who are unvaccinated (3% in vaccinated persons). Variola minor has a one to two percent fatality rate in unvaccinated individuals. There are two rare and more serious forms of smallpox. In the most severe, known as purpura variolosa or hemorrhagic-type smallpox, the initial stage of the illness (before the rash appears) is accompanied by a dark, purplish, blotchy flushing of the skin. People who developed purpura variolosa usually have a severe loss of blood into the skin and internal organs (hemorrhage), and die before the typical smallpox rash appears. About three percent of the persons with variola major develop purpura variolosa.

Another rare and deadly form of smallpox is referred to as flat-type smallpox affects about five percent of persons with variola major. Persons with this form of the disease have lesions that develop more slowly, never raised above the surface of the skin, and feel soft to the touch. If people with flat smallpox survive, they rarely experience severe scarring. Both purpura variolosa and flat smallpox are virtually never seen in persons infected with variola minor.

Smallpox can be confused with chickenpox, but several features of these diseases are significantly different:

  • The initial symptoms of smallpox are much more severe than those of chickenpox (i.e., high fever, severe muscle aches, etc.).
  • Smallpox rash is most common on exposed portions of the body: face, forearms, wrists, palms, lower legs, feet, and soles. (Chickenpox is most common on covered areas of the body.)
  • Smallpox rash lesions in one part of the body tend to be at the same stage of development. With chickenpox, it is common to have more than one eruption of pox lesions that are in different stages of development. Smallpox lesions tend to be deeper in the skin than chickenpox lesions, hard to the touch, and the vesicles are tough to break.

Smallpox is spread by an ill person releasing virus infected saliva droplets from their mouth into the air that are inhaled by a susceptible person in close contact with the ill person (face-to-face contact). Because virus amounts in saliva are highest during the first week of illness, this is when people are the most infectious. Disease is most often transmitted from the time the ill person first develops the rash throughout the first week of illness; however, the person is still infectious until the rash has resolved (all scabs have fallen off). Virus is also present in the scabs that separate from the skin but these are much less infectious than saliva.

There is a vaccine to prevent smallpox that was routinely administered in the United States until the early 1970s. Routine vaccination of the civilian population for this disease is not currently recommended. The risk of adverse events resulting from the vaccine, accompanied by the rapid decrease in smallpox around the world in the 1970s, was part of the justification for the U.S. to discontinue routine vaccination against smallpox before the disease was eradicated in 1977.

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 cause smallpox. Getting smallpox vaccine before exposure will protect about 95 percent of people from getting smallpox. Vaccination within three days of exposure will prevent or significantly lessen the severity of smallpox in the vast majority of people. Vaccination four to seven days after exposure likely offers some protection from disease or may modify the severity of disease.

Smallpox can be diagnosed based on the patient’s clinical signs and symptoms. The disease can be definitively diagnosed by isolation of the virus from the blood or lesions, or by identification of antibodies in the blood made in response to the virus. The diagnosis of smallpox needs to be made in specialized laboratories with appropriate testing techniques and measures to protect the laboratory workers. Clinicians who suspect smallpox in a patient must report the disease immediately to the OSDH Acute Disease Service at (405)271-4060 for investigation and coordination of testing to confirm the suspected diagnosis.

At this time, there is no proven treatment for smallpox. Patients with the illness would be given supportive therapy as needed and antibiotics for any secondary bacterial infections that occur. No antiviral medications have yet proved effective for treating smallpox. A smallpox outbreak would spread unless checked by vaccination and monitoring of contacts to smallpox patients and isolation of infectious smallpox patients. People with smallpox must avoid contact with unvaccinated individuals in order to prevent transmitting the disease to them. All individuals in who smallpox is suspected would be placed under health monitoring.

Smallpox Fact Sheets and Information:

Smallpox Fact Sheet (38k.pdf)

External Smallpox Resources:

PHB seal
Back to Top