Researchers Working on a Vaccine Against the Black Plague

The Black Plague?  Why would researchers work on a vaccine against a disease that no one gets anymore?  The plague, caused by the Gram-negative bacterium Yersinia pestis, is best known for the plague pandemic that decimated the population of Europe by a third in the 1300's. 

There is considerable interest in developing a vaccine against Yersinia pestis as it is among the list of "category A", highest priority microorganisms on the bioterrorism watch-list (along with Bacillus anthracis, Clostridium botulinum, Francisella tularensis, smallpox, and hemorrhagic viruses like Ebola).  There is a long history of military research and deployment of the plague as biological weapon.  For example, the former Soviet Union, during the Cold War, produced bombs to deliver Yersinia pestis to major US cities. The Japanese military dropped Yersinia pestis-infected fleas on parts of China during World War II. 

Progress on the vaccine has not been encouraging.  Recent studies still show unpredictable and only partial immunization. 

For a review of the use of plague as a biological weapon, check out this paper.