To control the spread of the virus, people who have smallpox would be kept in isolation at a hospital. All the people they've had contact with would receive the smallpox vaccine, which can prevent or lessen the severity of the disease if given within three days of exposure to the smallpox virus.

The vaccine uses a live virus that's related to smallpox, and it can occasionally cause serious complications, such as infections affecting the heart or brain. That's why a general vaccination program for everyone isn't recommended at this time. The potential risks of the vaccine outweigh the benefits, in the absence of an actual smallpox outbreak.

If you were vaccinated as a child

It's not known how long immunity lasts after a smallpox vaccine. Studies to answer that question have had conflicting results. The duration of protection can be affected by the type of vaccine used and how it was administered.

It's likely that vaccination is most effective for about three to five years, with immunity decreasing after that. Partial immunity may last much longer.

Aug. 10, 2011