1971 Aral smallpox incident

The Aral smallpox incident was a 30 July 1971 outbreak of the viral disease which occurred as a result of a field test at a Soviet biological weapons (BW) facility on an island in the Aral Sea. The incident sickened ten people, of whom three died, and came to widespread public notice only in 2002.

Source: Wikipedia — 1971 Aral smallpox incident (CC BY-SA 4.0)