AVA is classified as a subunit vaccine that is cell-free and containing no whole or live anthrax bacteria.[2] The antigen (immunologically active) portions are produced from culture filtrates of a toxigenic, but avirulent, nonencapsulated mutant — known as V770-NP1-R — of the B. anthracis Vollum strain.[3] (The Vollum strain was the same one weaponized by the old U.S. biological warfare program.)