Narrator: This is Science Today. Smallpox has probably caused more deaths from infectious disease than any other disease in history. The last case of smallpox in the world was reported in Ethiopia in 1976 and in 1980, scientists announced that vaccines had been successful at eradicating smallpox from the world. George Rutherford, director of the University of California, San Francisco's Preventive Medicine and Public Health Division, says previous assumptions that the disease could be easily controlled in the case of another outbreak were wrong.
Rutherford: This assumes that one hundred percent of the population is immune to smallpox. The correct number for that is zero percent.
Narrator: That's because the smallpox vaccine only protects for about twenty years and the U.S. stopped vaccinating civilians over thirty years ago.
Rutherford: So, basically nobody's immune anymore. Once you're exposed, you don't only have to use small pox before exposure-smallpox vaccine. You can use it after exposure as well. You have about a three- or four-day window. If you immunize somebody within that window three-to-four day method, you can prevent them from getting smallpox.
Narrator: For Science Today, I'm Larissa Branin.