Smallpox is a highly contagious -- and sometimes deadly -- disease. Fortunately, vaccination has played a crucial role in eliminating the disease worldwide. The vaccine provides three to five years of high-level immunity against smallpox, and decreasing immunity after that. Historically, the smallpox vaccine has been effective in preventing infection in 95 percent of those vaccinated. In addition, the vaccine helps prevent or substantially lessen infection when given within a few days of exposure.
Vaccination efforts among the American public were so successful that routine vaccination was stopped in 1972, after the disease was eradicated in the United States.
(To learn more about this topic, click Smallpox Vaccine. This article gives an overview of who should and should not get vaccinated, how the injection is given, and more.)