Instead, they used a strain specifically devised to defeat U.S. immunizations. This lethal strain had been developed years earlier by bioweaponeers in the former Soviet Union, using the U.S. vaccine as a tool in the search for a resistant strain. The bacterium Bacillus anthracis, the source of the anthrax toxin, is easily grown in large quantities. It is also cultured to make vaccine. To use anthrax as a weapon, dry spores are mixed with an aerosol dispersant.
Anthrax spores can lie dormant for decades, possibly for centuries.
Two extraordinary incidents attest to their durability. In 1942 British bioweaponeers carried out experiments with anthrax bombs on part of the island of Gruinard off the northwest coast of Scotland. Viable spores persisted for more than 40 years until the island was decontaminated in 1987 by literally soaking the soil with hundreds of thousands of liters of formaldehyde. Test data indicated that, without decontamination, viable spores would have persisted until at least 2050. I on suspicion of espionage and sabotage.