Thanks to a successful worldwide vaccination effort in the 20th century, smallpox has been wiped out. No one has gotten smallpox naturally since 1977. However, it is possible that variola virus (the virus that causes smallpox) could be used in a biological attack (an intentional release of viruses, bacteria, or other germs that can sicken or kill people, livestock, or crops). Public health authorities prepare for a possible but unlikely biological attack that uses smallpox as a weapon.