Smallpox
Variola - major and minor; Variola
Smallpox is a serious disease that is easily passed from person to person (contagious). It is caused by a virus.
Smallpox is a contagious disease caused by a virus. Smallpox virus has been eradicated worldwide through successful vaccination and treatment programs, and now exists only as a stored virus in a few research centers. Symptoms include a severe rash that leaves scars, fever, headache, vomiting and diarrhea.
Causes
Smallpox spreads from one person to another through saliva droplets. It may also be spread from bed sheets and clothing. It is most contagious during the first week of the infection. It may continue to be contagious until the scabs from the rash fall off. The virus can stay alive from 6 to 24 hours.
People were once vaccinated against this disease. However, the disease has been eradicated since 1979. The United States stopped giving the smallpox vaccine in 1972. In 1980, the World Health Organization (WHO) recommended that all countries stop vaccinating for smallpox.
There are two forms of smallpox:
- Variola major is a serious illness that can be life threatening in people who have not been vaccinated. It was responsible for a large number of deaths.
- Variola minor is a milder infection that rarely causes death.
A massive program by the WHO wiped out all known smallpox viruses from the world in the 1970s, except for a few samples saved for government research and presumed bioweapons. Researchers continue to debate whether or not to kill the last remaining samples of the virus or to preserve it in case there may be some future reason to study it.
You are more likely to develop smallpox if you:
- Are a lab worker who handles the virus (rare)
- Are in a location where the virus was released as a biological weapon
It is unknown how long past vaccinations stay effective. People who received the vaccine many years ago may no longer be fully protected against the virus.
THE RISK OF TERRORISM
There is a concern that the smallpox virus could be spread as part of a terrorist attack. The virus could be spread in spray (aerosol) form.
Symptoms
Exams and Tests
Tests include:
- Disseminated intravascular coagulation (DIC) panel
- Platelet count
- White blood cell count
Special lab tests can be used to identify the virus.
Treatment
The smallpox vaccine may prevent illness or lessen symptoms if it is given within 1 to 4 days after a person is exposed to the disease.
In July 2013, a shipment of 59,000 courses of the antiviral medicine tecovirimat was delivered by SIGA Technologies to the United States Government's Strategic National Stockpile for use in a possible bioterrorism incident with smallpox.
Antibiotics may be given for bacterial infections that occur in people who have smallpox. Taking antibodies against a disease similar to smallpox (vaccinia immune globulin) may help shorten the duration of the disease. It may also reduce the risk of death in a rare form of smallpox that occurs in people with eczema.
People who have been diagnosed with smallpox and people they have been in close contact with need to be isolated right away. They will need to receive the vaccine and be watched closely.
Outlook (Prognosis)
In the past, this was a major illness. The risk of death was as high as 30%.
Possible Complications
Complications may include:
- Arthritis and bone infections
- Brain swelling (encephalitis)
- Death
- Eye infections
- Pneumonia
- Scarring
- Severe bleeding
- Skin infections (from the sores)
When to Contact a Medical Professional
If you think you may have been exposed to smallpox, contact your health care provider right away. Contact with the virus is very unlikely unless you have worked with the virus in a lab or you have been exposed through bioterrorism.
Prevention
Many people were vaccinated against smallpox in the past. The vaccine is no longer given to the general public. If the vaccine needs to be given to control an outbreak, it can have a small risk of complications. Currently, only military personnel, health care workers, and emergency responders may receive the vaccine.
References
Centers for Disease Control and Prevention website. Smallpox.
James WD. Viral diseases. In: James WD, ed. Andrews' Diseases of the Skin: Clinical Dermatology. 14th ed. Philadelphia, PA: Elsevier; 2026:chap 14.
Petersen BW, Damon IK. Orthopoxviruses: vaccinia (smallpox vaccine), variola (smallpox), monkeypox, and cowpox. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 132.
Petersen BW, Damon IK. Smallpox, monkeypox, and other poxvirus infections. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 343.
Version Info
Last reviewed on: 4/1/2025
Reviewed by: Elika Hoss, MD, Assistant Professor of Dermatology, Mayo Clinic, Scottsdale, AZ. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
