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Smallpox

Summary

Smallpox: is a highly contagious and deadly disease that is caused by the variola virus. The last case of smallpox in the world was in 1977.

Symptoms: the disease begins with high fever, malaise, head and body aches, and sometimes vomiting. This is followed by a rash that turn into bumps and then postules, which form a crust and scab. People are contagious until all the scabs have fallen off.

Smallpox vaccine: is made with live vaccinia virus. The vaccine cannot cause smallpox, but the vaccinia virus can cause serious and even life-threatening effects in some people.

What is smallpox?

Smallpox* is a highly contagious and deadly illness caused by the variola virus. The most common form of smallpox kills about 30 percent of those who are infected. There is no specific treatment for smallpox. The last case of smallpox in the United States appeared in 1949, and the last naturally occurring case in the world was in 1977. Except for laboratory stockpiles, the smallpox virus has been eliminated. Concern that others may have acquired the variola virus has prompted the government to increase preparations against the possibility of an intentional release of smallpox.

*The information presented here is based on what is known about smallpox in its natural form.

What are the symptoms as the disease progresses?

After exposure, it takes between 7 and 17 days for symptoms of smallpox to appear (average incubation period is 12 to 14 days). During this time, the infected person feels fine and is not contagious. The early symptoms of smallpox (prodrome phase) begin with high fever, head and body aches, and sometimes vomiting, and the person may be contagious. At this time, people are usually too sick to carry on their normal activities. Early rash lasts about 4 days, at which time the person is most contagious. The rash progresses to postules and eventually scabs. When all lesions have formed scabs and fallen off, the person is no longer contagious.

How is smallpox spread (transmitted)?

Naturally occurring smallpox normally spreads from contact with infected persons by direct and fairly prolonged close (within about 6 feet) face-to-face contact. Smallpox also can be spread through contact with infected bodily fluids or contaminated objects such as bedding or clothing. The individuals most at risk of catching the disease are unvaccinated people who live in the same house or those caring for patients with smallpox.

How was smallpox eliminated from the world?

The successful worldwide smallpox eradication effort employed a strategy that included the identification, isolation, and vaccination of people with smallpox and their close contacts.

Factors That Aid In Controlling the Spread of Smallpox

There are characteristics of the disease that were important in the successful effort to eliminate smallpox and would aid in the control of a future outbreak. These include:

  • All individuals who get smallpox have symptoms.
  • Smallpox makes people very sick and they are unable to carry out their normal activities.
  • Generally, fairly prolonged face-to-face contact is required to spread smallpox from one person to another.
  • Humans are the only natural hosts of variola. Smallpox is not known to be transmitted by insects or animals.
  • The vaccine is highly effective when given prior to exposure. In addition, vaccination within 3 days of exposure will completely prevent or significantly modify smallpox in the vast majority of persons. Vaccination 4 to 7 days after exposure likely offers some protection from disease or may modify the severity of disease.

If cases were to appear, treating facilities would need to use certain infection control and worker protection measures. These include isolating suspected and confirmed cases in rooms that are under negative air-pressure, and providing workers with respiratory protection.

Is the smallpox vaccine effective safe?

The vaccine is made with a live virus called vaccinia. The vaccine cannot cause smallpox.However, the vaccinia virus can cause serious and even life-threatening side effects. Routine vaccination was stopped in the U.S. in 1972. The smallpox vaccine provides a high level immunity for 3 to 5 years. The effectiveness fades after 5 years and is probably negligible after 20 years. Revaccination provides longer lasting immunity. See the AFSCME Fact sheet —Smallpox Vaccine: What Workers Need to Know Before Volunteering to Be Vaccinated — for more information about the smallpox vaccine and related safety and workplace concerns.

February 14, 2003

For more information about protecting workers from workplace hazards, contact the AFSCME Health and Safety Program at (202) 429-1215, or 1625 L Street, N.W., Washington, DC 20036.

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