[Smallpox, an old foe].

Smallpox has accompanied mankind for centuries, causing deaths and permanent lesions. Used in the past as a biological weapon during wars, it has come into focus again precisely because of this renewed possibility, although the disease has been eradicated in the Americas since 1971 and worldwide since 1977. Data gathered during the eradication campaigns show that the disease spread relatively slowly through close contacts between patients and susceptibles. Sub-clinical infection in non-vaccinated individuals was a rare event, and blockade vaccination surrounding new cases (as long as these cases were confirmed early) was able to prevent the disease from spreading in the community. Even with only one dose, vaccinated individuals rarely developed a serious case of the disease upon reinfection. The use of smallpox as a biological weapon should be considered a real possibility, although according to the available data, highly virulent viral suspensions spread very close to the target population would be necessary to infect a large number of persons.