Only one human study, conducted in wool-sorters who handled anthrax-contaminated goat hair, has ever proven that the vaccine actually protects people, and it's unclear whether its ability to prevent skin infections in those workers would apply if a terrorist unleashed a weaponized version of the bug that was inhaled. (Still, the vaccine did work in the study, and it's odd that Matsumoto mentions it only in passing.) Some reputable scientists question whether the vaccine contains the right ingredients to effectively thwart the many strains of anthrax that exist. On top of these issues, the vaccine's manufacturer has a long history of run-ins with the FDA over quality-control issues at its aging manufacturing plant.