Today in History - April 2: A few milligrams from lab leak killed dozens of people

A northeasterly wind scattered a few milligrams of anthrax spores from a military facility in the Soviet city of Sverdlovsk on April 2, 1979.

The spores settled over the edge of the city and nearby villages, killing at least 66 people and likely many more.

Worst affected was a nearby ceramics factory, where a ventilation system sucked in air from the outside.

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Workers at the factory were directly exposed through the ventilation system, killing at least 18 people.

But the Soviets denied a lab leak, telling the world the deaths were caused by tainted meat.

The US government was suspicious of the Soviet explanation and publicly accused them of a cover-up.

The USSR responded angrily to the claims.

The truth was not made public until 1992 by President Boris Yeltsin.

As head of the Sverdlovsk Communist Party in 1979, Yeltsin had known the truth the whole time.

The leak was later attributed to workers forgetting to replace a filter in an exhaust system.

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If the wind had been going in the opposite direction that day, it is estimated hundreds of thousands could have died.

Northern Arizona University geneticist Paul Keim later led a team to map the DNA code.

His study found the anthrax was developed to be as deadly as possible.

"All of this is highly suggestive of a weapons program that identified a suitable strain, maintained master cell stocks to avoid extensive passage, and performed minimal manipulations in order to maintain virulence," his study said.

"This strategy must have been used to produce large quantities of highly virulent material, as evidenced by the anthrax deaths in 1979."

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The Soviets had long denied conducting experiments into biological weapons.

Sverdlovsk is now known as Yekaterinburg.

Anthrax is a bacterial disease that occurs sporadically in livestock.

Without treatment, the mortality rate 100 per cent.