Alternative names
Variola - major and minor; Variola

Smallpox is a viral disease characterized by a skin rash and a high death rate.

Causes, incidence, and risk factors

Smallpox was once found throughout the world, causing illness and death wherever it occurred. Smallpox was primarily a disease of children and young adults, with family members often infecting each other.

A massive program by the World Health Organization (WHO) eradicated all known smallpox viruses from the world in 1977, except for samples that were saved by various governments for research purposes. The vaccine was discontinued in the United States in 1972. In 1980, WHO recommended that all countries stop vaccinating for smallpox.

In 1980, WHO also recommended that the remaining virus samples be transferred to two WHO laboratories for storage. Those laboratories were the Centers for Disease Control (CDC) in Atlanta, Georgia, and a laboratory in Russia. Russia, however, started a program to produce the smallpox virus in mass quantities, specifically for bombs and other weaponry.

Some believe that other countries such as Iraq, Iran, and North Korea may also hold some stores of the smallpox virus. 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.

According to the CDC, since the vaccine has not been administered in the U.S. since 1972, those persons who had received the vaccine in the past are likely susceptible now (as are those who have never been vaccinated). It is not known how long previous vaccinations would remain effective, but it is unlikely that people would still have a high enough level of immunity to protect against the virus.

Risk factors for smallpox include being a laboratory worker who handles the virus (rare), or being in the environment where the virus was released as a biological weapon.


It is conceivable that smallpox could be deliberately reintroduced into the population. Smallpox could be released by aerosol, and it would spread easily because the virus remains very stable in aerosol form.

It would take no more than 50-100 cases to cause legitimate concern on an international level. Emergency measures would need to be taken immediately.

Smallpox is highly contagious from one person to another. It is most contagious during the first week, and is spread from saliva droplets. It may continue to be contagious until the scabs from the rash fall off. It may also be spread from bed sheets and clothing.

Researchers believe that the smallpox infection (if released in aerosol form, under favorable conditions, without sunlight) could remain viable for as long as 24 hours. In unfavorable conditions, the virus may only remain viable for 6 hours. There is clear evidence that shows that the virus can remain viable on bed linens and clothes for significant periods of time.


Smallpox has two forms: 1) Variola major - which is a serious illness with a mortality rate according to the CDC of 30% or more, in unvaccinated people, and 2) Variola minor - a milder infection with a mortality rate of less than 1%. The incubation period for smallpox is approximately 12-14 days. The symptoms are:

  • High fever  
  • Fatigue  
  • Severe headache  
  • Backache  
  • Malaise  
  • Rash, raised and pink on the skin, starting centrally and spreading outwards. (First the mucosa of the mouth and throat, then face, forearms, trunk, and legs. Rash turns to pus-filled lesions that become crusty on the eighth or ninth day.)  
  • Delirium  
  • Vomiting and diarrhea  
  • Excessive bleeding

Signs and tests

  • Virus can be seen by electron microscope and by culture.  
  • Low white blood cell count initially, that increases later in the disease.  
  • Low platelet count.  
  • DIC panel can be positive in cases of hemorrhage.  
  • Antibodies turn positive soon after the infection is complete.


If the smallpox vaccination is given within 1-4 days of exposure to the disease, it may prevent illness, or at least lessen the degree of illness associated with the disease. Treatment, once the disease symptoms have started, is limited.

There is no agent that has been specifically made for treating smallpox. Sometimes antibiotics are given for secondary infections that may occur. Vaccinia immune globulin (antibodies against a disease similar to smallpox) may help shorten the disease.

If a diagnosis of smallpox were made, exposed persons would need to be isolated immediately. The isolation would include not just the person who contracted the disease, but all other face-to-face contacts with that person.

These individuals would need the vaccine and need to be monitored. Emergency measures to protect a broader segment of the population would have to be implemented immediately, within the recommended guidelines from the CDC and other federal and local health agencies.

Expectations (prognosis)
In the past, this was a major illness with significant mortality as high as 30%.


  • Bacterial infections at the skin at the sites of the lesions  
  • Pitted scars from pustules  
  • Arthritis and bone infections  
  • Pneumonia  
  • Severe bleeding  
  • Eye infections  
  • Brain inflammation (encephalitis)  
  • Death

Calling your health care provider
If you think you may have been exposed to smallpox, contact your health care provider immediately. Since smallpox has been eradicated, this would be very unlikely, unless you have worked with the virus in a laboratory or there has been an act of bioterrorism.


Many people were vaccinated for smallpox in the past - but the vaccination is no longer given because the virus has been eradicated. According to the CDC, the United States has supply of the smallpox vaccine sufficient for the entire population at this time.

There are some complications associated with the vaccine, should the vaccine need to be given in the future to control an outbreak. Some of these are easily treated rashes, while other potential complications are more serious. The risk of complications is relatively low. (For example, the chance of encephalitis, which could be a fatal complication, is 1 out of 300,000).

When smallpox was eradicated, the general population was no longer vaccinated because the potential complications and costs began to outweigh the benefits of taking it. The experience of vaccination of both military personnel and civilian health care workers in 2002-2003 suggested that the risk was very low but nonetheless present, and very small numbers of people had unforeseen reactions.

Smallpox vaccination is not currently being done for members of the general public. As of mid-2003, any further vaccination outside of military personnel is likely to be done, in a closely supervised fashion, in health care workers and emergency responders. There is ongoing review of smallpox vaccination, including the current and newer vaccines.

Johns Hopkins patient information

Last revised: December 4, 2012
by Amalia K. Gagarina, M.S., R.D.

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