Smallpox is an infectious disease caused by a virus similar to the one that causes chickenpox. Smallpox was eliminated from the world as a result of widespread vaccination. There has been no vaccine given for smallpox since 1972. People who were immunized against smallpox before 1972 are no longer protected from this illness.
If you are exposed to a known case of smallpox, the vaccine can reduce the severity or possibly prevent the illness if given within 4 days after exposure. The vaccine is effective up to 7 days after exposure. Symptoms occur within 1 to 2 weeks after exposure. Symptoms begin with high fever, fatigue, and headache for 2 to 4 days. A rash starts as small red spots on the tongue and in the mouth. These spots change into sores which break open and spread large amounts of virus into the mouth and throat. This rash then usually spreads to all parts of the body within 24 hours. The spots become blisters and fill with pus. The blisters then break open and crust over.
Smallpox is spread from person to person by saliva during close contact and by contact with the fluid from the skin rash. The virus also spreads when coughed or sneezed droplets from the nose or mouth spread to others. The contagious period begins when symptoms appear. This may be 2 to 3 days before the rash starts, however the most contagious stage is when the rash appears. The disease remains contagious until all scabs have dried and fallen off (about 3 to 4 weeks).
What to know about exposure
If you are exposed to a known case of smallpox, contact your healthcare provider or your local public health department for advice. An exposed person cannot give the disease to another person unless the symptoms of illness are present.
If you think you have symptoms of smallpox:
Don't have contact with others.
Call your local hospital, clinic, or healthcare provider's office. When you call, you will be told how to be examined for the disease without exposing others.
For latest information about smallpox and other infectious disease, see the CDC web site at www.cdc.gov. Search for "smallpox." You can also contact your county public health department.