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Smallpox is a highly contagious disease that is caused by the variola virus. Initial symptoms of this disease are similar to those of a flu, but a characteristic rash will typically follow within days. Although outbreaks used to be common, a vaccine was eventually created, and the disease was eradicated worldwide by 1980.

What Is Smallpox?

Smallpox is a serious, highly contagious, and sometimes fatal disease. The name smallpox is derived from the Latin word for "spotted," which refers to the raised bumps that appear on the face and body of an infected person.
Thanks to the success of vaccination, the last natural outbreak of smallpox in the United States occurred in 1949. By 1972, routine vaccinations for children in the United States were no longer needed. In 1980, the disease was said to be wiped out worldwide, and no cases of naturally occurring smallpox have occurred since then.

What Causes It?

The cause of smallpox is an infection with the variola virus.
Variola virus is a double-stranded DNA virus in the family Poxviridae and the genus Orthopoxvirus. Variola virus only infects humans.
(Click Cause of Smallpox for more information on this topic.)

Different Types of Smallpox

There are 2 clinical forms of smallpox: variola major and variola minor. Variola major is the severe and most common form of smallpox, characterized by a more extensive rash and higher fever. There are 4 types of variola major smallpox:
  • Ordinary (the most frequent type, accounting for 90 percent or more of cases)
  • Modified (mild and occurring in previously vaccinated persons)
  • Flat
  • Hemorrhagic.
Both flat and hemorrhagic are rare and very severe conditions.
Historically, variola major has an overall mortality rate of about 30 percent. Flat and hemorrhagic smallpox are almost always fatal. Variola minor is a less common presentation of smallpox, and a much less severe disease, with death rates historically of 1 percent or less.
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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