Smallpox is a serious and contagious disease that causes a rash on the skin.

Smallpox was once found throughout the world, causing illness and death wherever it occurred. It mainly affected children and young adults. Family members often infected each other.

There are two forms of smallpox:

• Variola major is a serious illness that can be life threatening in people who have not been vaccinated
• Variola minor is a milder infection that rarely causes death

It usually takes 12 - 14 days after a person has been infected for symptoms to appear.

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

In 1980, the WHO also recommended that the remaining virus samples be sent 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 large amounts for weapons. Some people believe that other countries 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.

The vaccine has not been given in the U.S. since 1972. According to the CDC, people who received the vaccine in the past and those who have never been vaccinated could be at risk. People who were vaccinated many years ago are not likely to have a high enough level of immunity to protect against the virus. It is not known how long past vaccinations stay effective.

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

THE RISK OF TERRORISM

Smallpox could be deliberately spread by aerosol. It would spread easily because the virus stays very stable in aerosol form.

It would take no more than 50-100 cases of smallpox to cause international concern. Emergency measures would need to be taken immediately.

Smallpox spreads easily from one person to another from 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.

Researchers believe that the smallpox infection might be able to stay alive (under the right conditions) for as long as 24 hours. In unfavorable conditions, the virus may only remain alive for 6 hours. There is clear evidence that the virus can remain alive on bed linens and clothes for long periods of time.